I tried to (unsuccessfully) blow a sugar bowl yesterday - I ended up moulding it into a fish-bowl shape with my fingers (dang that sugar is HOT)....so I wanted to use it as a fish bowl but then got to wondering if Piping gel & the hardened sugar will react when put together? (I want it to look like water in the fish bowl - & then the second issue - will a fondant fish survive in the piping gel?)
no one was really sure what do to with piping gel on isomalt so I decided to just not use any (I even emailed the U.K. to see if they would know - they didn't but were eager to see how it worked!)
I did the bowl & put the fish poking out, made some little blue pebbles & a little bridge for the fish to swim under - its my Sesame street cake if you are interested in seeing the final product
Have thought about posting you question in the MYOM forum. Dominic, (creator of make your own mold) might be able to answer your question.