There is a book i used to read as a kid called "Memoirs of a Sword Swallower" and in it he dabbles in the regurgitating thing.
He used the method you have already written about, he would tie a piece of FOOD (thats a good thing to take note of) to it and pull it up while trying to force it up with his stomach muscles and so on.
I know a couple of bulimics who can do it on command simply by thinking about it but i would suggest the first method of practise.
Just while that reminds me, pulling something up passed your gag reflex will often make one vomit by default, for this reason i would suggest having a completely empty stomach before attempting your practise. Side effects of stomach acid coming up in this way include loss of tooth enamel (not a good look) and tears in the eosaphagus (not a good feeling) and many more.
Keep us posted.