Now you can already Spellstrike with other maneuvers like trip, that is because Trip/Disarm/Sunder attempts can be done in place of a melee attack
Dirty Trick on the other hand is a standard action
You can attempt to hinder a foe in melee as a standard action.
Which means it can't be (currently..maybe)
The Quick Dirty Trick Feat
On your turn, you can perform a single dirty trick combat maneuver in place of one of your melee attacks. You must choose the melee attack with the highest base attack bonus to make the dirty trick combat maneuver.
Does that mean that I can now Dirty Trick with a Spellstrike?
Does that mean that I can now Dirty Trick with a Spellstrike?
Not in general. Spellstrike has a specific limitation: "magus can make one free melee attack with his weapon" - a dirty trick is usually not an attack made with a weapon.
You can perpetrate a dirty trick and deliver an attack before your opponent is the wiser.
Prerequisite: Int 13, Combat Expertise, Improved Dirty Trick, base attack bonus +6.
Benefit: On your turn, you can perform a single dirty trick combat maneuver in place of one of your melee attacks. You must choose the melee attack with the highest base attack bonus to make the dirty trick combat maneuver.
Normal: A dirty trick combat maneuver is a standard action.
At 2nd level, whenever a magus casts a spell with a range of “touch” from the magus spell list, he can deliver the spell through any weapon he is wielding as part of a melee attack. Instead of the free melee touch attack normally allowed to deliver the spell, a magus can make one free melee attack with his weapon (at his highest base attack bonus) as part of casting this spell. If successful, this melee attack deals its normal damage as well as the effects of the spell. If the magus makes this attack in concert with spell combat, this melee attack takes all the penalties accrued by spell combat melee attacks. This attack uses the weapon’s critical range (20, 19–20, or 18–20 and modified by the keen weapon property or similar effects), but the spell effect only deals ×2 damage on a successful critical hit, while the weapon damage uses its own critical modifier.
Quick Dirty Trick doesn't just replace one of your attacks like Trip/Disarm/Sunder. Trip/Disarm/Sunder can replace any of your iterative attacks or even an attack of opportunity, but Quick Dirty Trick can only replace your highest BAB attack you make in a round.
Normally you're performing a Dirty Trick without a weapon; i.e. kicking dirt or throwing sand in the eyes to blind, kneeing them in the unmentionables to sicken/nauseate, or pulling their pants down to entangle, and so on, etc. So no, you cannot deliver a touch spell through your weapon when you're performing a Dirty Trick like this.
So there's a couple of things at work here, Spellstrike is an attack made at your highest BAB, and QDT must be used on your Highest BAB attack. Many GM's will read this and say no. It depends on what your GM will let you get away with and how you and your GM interpret these rules.
Here's how you can make your case to your GM:
Your Weapon can hold Touch Spell charges, so if you use Spellstrike to perform a Touch Spell and put it in your weapon, and then you decide to perform a Quick Dirty Trick in lieu of your Highest BAB attack, and that weapon touches the target while you're performing a Quick Dirty Trick, then presto, you delivered your spell.
Holding the Charge: If you don’t discharge the spell in the round when you cast the spell, you can hold the charge indefinitely. You can continue to make touch attacks round after round. If you touch anything or anyone while holding a charge, even unintentionally, the spell discharges. If you cast another spell, the touch spell dissipates. You can touch one friend as a standard action or up to six friends as a full-round action. Alternatively, you may make a normal unarmed attack (or an attack with a natural weapon) while holding a charge. In this case, you aren’t considered armed and you provoke attacks of opportunity as normal for the attack. If your unarmed attack or natural weapon attack normally doesn’t provoke attacks of opportunity, neither does this attack. If the attack hits, you deal normal damage for your unarmed attack or natural weapon and the spell discharges. If the attack misses, you are still holding the charge.