I like the idea of stealing spells, but I'm more interested in the sorcerer or witch class than the bard. Is it possible to take a one level dip into the Sandman archetype for the stealspell ability and utilize your primary class's spell slots to fuel the ability? For example, a Wizard 10 / Sandman 1 would be able to steal fifth level spells, since it's the highest level that he can cast.
Stealspell (Su): A sandman can use performance to steal spells from his foes and add them to his list of spells known. Once the performance is started, the bard can steal a prepared spell or a spell known from another creature with a touch attack as a standard action. The target receives a Will save (DC 10 + 1/2 the bard’s level + the bard’s Cha bonus) to negate the effect. The sandman may choose a spell to steal, but if the target does not possess the spell, the bardic performance immediately ends. Otherwise the spell stolen is random, but it is always of the highest level that the bard can cast, if possible. The target loses the prepared spell or spell known and the sandman adds it to his list of spells known for as long as the performance continues, after which it reverts to the original recipient. While stolen, the bard can cast the spell using his available spell slots. This use does not consume the stolen spell. If the bard steals another spell while a spell is stolen, the previous spell immediately reverts to its original owner. This ability requires visual components.
I'm worried that because the bolded bit refers to the bard or sandman, that you're restricted to using their spell slots for the ability, but I can't find evidence for this. Although many classes will refer to class levels when setting the DC of an ability, this is a different kind of case and it could just serve the purpose of referring to the character. Do the rules say anything definite about this?