Yes Gallium has been used in tricks before. The one I know of is a spoon that dissolves in hot water/liquid. Various applications for that.
NOTE - Gallium is NOT to be consumed. I can't remember the exact composition, but I'm pretty sure it's significantly lead and I know it is toxic. So if you do something like letting a spoon dissolve in coffee (a presentation I have seen) do NOT drink that coffee.
Also note - the melting point of gallium is quite low. Depending on where you live, you may only be able to use it during the coldest months of the year. I know a guy in CA who had to literally change the percentages of various components of gallium-based gimmicks because the atmospheric temperature was higher than the melting point of said gimmicks for most of the year.