I dont suppose you have any consideration of the Summoner, in particular the synthesist? Charisma based arcane caster, put on your eidolon gundam and go kick butt? Its not quite transforming into, but you certainly become something bestial.
Also how are you on 3rd party options? There are a bunch of ways to be a combat focused arcane caster in the 3pp realms if you are able to use them.
Ok, so I wanted to play something kind of off the wall in a campaign where most of the characters seem to be martial. The idea is a sorcerer who emphasizes melee combat by using shapechanging spells and buffs to wade into the fray and throw punches, maybe with some support spells like glitterdust and such to disorient and confuse opponents.
Is there any viable way to do a build like this with sorcerer or any other arcane caster?
Sorcerer with Draconic Bloodline into Dragon Disciple is made for exactly this.
You want your starting stats to be around this - Str 16-18, cha 14-16, con 12-14. If you have a 25pt buy and a floating +2 racial modifier you can have stats that look like -
16 str
14 dex
14 con
12 int
8 wis
16 cha
Which in my opinion is roughly the best way to start, but you can flavor to taste. Depending on desire, rolls and/or point buy used you may want to or need to nudge numbers around. The first couple of levels actually aren't bad. You'll need to be a little cautious but you can enter melee if there is a good opportunity. Pick spells like grease, colorspray and mage armor for 1st level spells. Mirror Image and Glitterdust as 2nd level spells.
I wouldn't focus heavily shapeshifting spells, but having something like Alter Self might be nice, especially if you run out of claw usage. You can also get a bite attack and a strength bonus a little early that way.
It will be less good at the low-mid levels (4-6) but you are still a sorcerer and can contribute just fine. It improves at 7th level (assuming that you immediately entered DD) which is when you get a free +2 str bonus and your third attack that does 1.5xstr. It just continues to get better from there. If you hit level 12 you will feeling pretty good with Form of the Dragon as a spell-like ability. You don't necessarily need high BAB when you're rocking 30+ str and have three attacks at your full bonus, and a couple of secondary natural attacks to boot as well.
I definately agree that the Dragon Disciple is a great option. Definately check out Osterisk's Guide to the Dragon Disciple. Even if you don't opt for the prestige class, he covers the benefits of strength, effective multiclcass combos, what spells to cast and the like. It should be at least a little helpful but...
The original concept, to be specific, was a guy who sort of had an old school pugilist feel
I don't know if the claws and bite attack would necessarily fit this... The problem with sorcerer is that it's so tied thematically with its bloodline and nothings really jumping out at me. Arcane bond with a weapon is a deceptively good deal, so a wizard or arcane sorcerer with a bonded pair of cestus might be worth checking out... though you are going to look like a bit of a chump if the GM ever takes your magic boxing gloves away. :P
As another possible concept, check out the Efreeti bloodline for a straight or multiclassed Sorcerer, its ninth level ability is amazing. Essentially you can turn into an Efreeti as a 13th level spell... 5 levels early at level 9. Beyond that you'd be a bronzed, genie blooded, Qadiran with fire-damage shocking grasps, enlarge person and plenty of buffing power. You could even play it up as a full-blown genie bound to another PC who owns your lamp.