Spellcraft + Bluff to bluff specific castings

[Dalebert]

So I had a thought. I have an item that lets me cast Ghost Sounds unlimited and Silent Image once a day. If I were trying to fool someone reasonably intelligent, could I potentially use my spellcraft knowledge and bluff to sort of seem like I'm casting a specific spell to help the illusion along? For instance, there are many spells that I don't actually know how to cast myself but that I have a chance to recognize due to spellcraft. Opponents with spellcraft have a chance to recognize a spell I'm casting that they don't have intimate knowledge of, i.e. don't know how to cast themselves. Presumably we are simply recognizing some key defining aspects of the spell. For instance, maybe there are some recognizable words or gestures that are common for earth spells, certain others for wall spells, and someone might conclude that a spell is probably Wall of Stone. Could I potentially mock cast while using a magic item to cast Silent Image, using a bluff check, so that they might be led to believe I am casting Wall of Stone and then I create an illusion of a stone wall? How reasonable or not is this notion? Am I stretching the limits of these skills to even suggest such a thing?

[jiriku]

I think that probably exceeds the capability of the unaided Bluff skill, but it's prime territory for a homebrewed skill trick, feat, spell, or alternate class feature.

[Troacctid]

No need for homebrew, it's an actual skill trick. False Theurgy, Complete Scoundrel p86. Requires 8 ranks in Spellcraft and 8 ranks in Bluff or Sleight of Hand.

[Dalebert]

No need for homebrew, it's an actual skill trick. False Theurgy, Complete Scoundrel p86. Requires 8 ranks in Spellcraft and 8 ranks in Bluff or Sleight of Hand.

That seems reasonable. Still, it seems to me you could always try it and the DM could apply modifiers to the difficulty depending on the situation. For instance, I could picture the skill trick being necessary if you were trying to fool someone who actually knows the spell but if they're just using spellcraft to figure it out, how likely are they to realize "Hey, he's not casting that right!". Spellcraft seems like a very broad skill. The idea of it has always been a bit weird for me. You obviously don't know how to cast all those spells so exactly how much do you know?