Before Jason had made his announcement, I had come up with a class ability rule for the Fighter to gain the Craft Arms & Armor feat and using his class levels as caster levels, and ways of bypassing the spell requirements, etc.
Then Jason reveals the following feat:
Master Craftsman
Your superior crafting skills allow you to create simple magic items. Choose one Craft or Profession skill in which you possess at least 5 ranks.
Prerequisites: 5 ranks in any Craft or Profession skill.
Benefit: Ranks in your chosen skill count as your caster level for the purposes of qualifying for the Craft Arms and Armor and Craft Wondrous Item feats. You can create magic items using these feats, substituting your ranks in the chosen skill for your total caster level. You must use the chosen skill for the check to create the item. The DC to create the item still increases for any necessary spell requirements (see the magic item creation rules in Chapter 15). You cannot use this feat to create any spell-trigger or spell-activation item.
Normal: Only spellcasters can qualify for the Craft Arms and Armor and Craft Wondrous Item feats.
This simultaneously does exactly what I was going to try and do, AND reveals a general mechanic overhaul for crafting magic items (yay!).
So the only thing missing was the following Fighter class ability:
Focused Craftsman
At 1st level, a fighter selects one Craft skill. He gains 1 bonus skill point to place in that Craft skill and an additional skill point every time he gains a level. In addition, a fighter adds 1/2 his level (minimum 1) to all Craft skill checks.
This bypasses the need for giving higher base skillpoints for the Fighter, while maintaining the class as a good choice for non-magical crafting. Besides, it makes sense that the Fighter would be the one making or repairing weapons and armor (as opposed to the Barbarian, Paladin or Ranger, who already have fairly specific themes).
.
My other idea was to give him some bonuses related to the "Engineering" side.
Yeah, basically I took the iconic "Dwarven Fighter" to get ideas on what to give him outside combat.
Engineering Tactics
At 1st level, a fighter adds 1/2 his level (minimum 1) to Knowledge (engineering) and Profession (siege engineer) skills. In addition, he may make Knowledge (engineering) checks untrained.
Upon reaching 3rd level, the fighter may roll a Knowledge (engineering) check against the Break DC to break through walls and doors.
This means a Fighter who puts points into this skill can, at 3rd level, rolls a +7 (plus any Int bonus) towards break DCs.
To put this in perspective: A Fighter with a 13 Int would roll an average of 19 (11+7+1). This is enough to blast through a Locked Good Wooden door more than 50% of the time.
By 9th level, he'll likely have (with a 14 int), a bonus an average roll of 29 (11+16+2). This gives a better than average chance to break through a wizard's Wall of Stone or Ice at those levels, and can attempt to break through a Wall of Iron two level later.
It also means that by 20th level, he's challenging all but the magically reinforced Masonry walls, which is fitting for a nigh-epic Fighter.
At the very least, even a Fighter that doesn't dedicate many (or any) points in the skill, can still roll a check in response to a Collapse or Cave-In situation.