Summons are usually strong hearts who have lost their worlds. I don't think any worlds have been destroyed yet. But on the other hand there is also Genie in KH2 and KH1 and tinkerbell in KH1. And since Neverland is definitely going to be in BBS, and its speculated that Agrabah is going to be in it too. So there could be a way, but I think you'd have to use Stitch's red ship.
By the way, how does TAV get to the other worlds. Do they use gummi ships?
Oh and Auron, I never said to totally get rid of Boo. There could be a second mission speciffically meant for you to be protecting Boo. And if not that, she would definitely be in the credits, chasing Sully and Mike around there apartment.
But I think this is a little off topic, anywho I believe Toy Story would be awesome. I would put Terra in Sids room, among those mutilated toys. Auqa would be in Andy's room where first the green army men mistake her for the "mysterious assailant". When she proves she is not, by spying on Andy's party, she's welcomed by Woody. Then she tells of a new toy Buzz Lightyear. THen the mysterious assailant attacks. Its a Jack in the box unbirth.
With Ven he goes to Pizza planet. He goes in toy mode. He thinks to himself he doesn't like the look of those robots in front. Then a soda cup and burger box lands on him. He runs after the two people who did that. He chases them into the cafeteria where Ven saves them from the alien soda fountains. Pizza planet has become and unbirth