You've mentioned that your friends typically min/max, but just to be clear, roughly what power level do they tend to play at? Can you describe what you think they will want to play as?
In any event, 'Support' to me screams Bard. Or, in your case, Bardsader. This won't be as powerful as a well played Wizard/Crusader/JPM, but you will be able to contribute in combat. If you were allowed 2 prestige classes, I'd suggest Bard 7/Crusader 2/JPM 1/Sublime Chord 1/JPM 2->10. This would get you essentially sorcerer spell casting (with level 9 spells, but one level behind the sorcerer), level 8 maneuvers, and up to +9-14d6 sonic damage inspire courage (depending on how much you optimise).
As you can only have one prestige class, you may want to look at a basic Bardsader: Bard 4/Crusader 16. Take Dragontouched, Dragonfire Inspiration, Draconic Heritage (Battle or Pyroclastic), Words of Creation, Song of the White Raven, Extra Granted Maneuver, and another feat of your choice. Also, make sure that you play a masterwork mandolin and wear a Vest of Legends. The first round of any given combat will probably consist of you using a swift action to inspire courage (with Dragonfire Inspiration and Words of Creation) to give everyone in your party +9-10d6 sonic damage (albeit at the cost of taking 3d4 nonlethal yourself), stopping the song as a free action, then using your standard action to inspire courage (with Words of creation) giving them a +9-10 morale bonus to their attack and damage rolls (taking another 3d4 nonlethal damage), and finally using your move action to find an advantageous position. In subsequent rounds, you can go to town with the standard Crusader maneuvers. They'll probably outshine you in combat, but you'll know that it was largely because of your buffs.