I had this problem with one of my sponsors. Long story short (as ive posted it a few times in recent weeks lol), a sponsor wanted the preloader loading bar showing while the preloader was doing its thing (in this case, cpmstar), but it doesnt work like that as you know. His argument was that people on a slower connection cant tell whether the game has finished loading (or crashed or something). He also wanted a button to appear once it had finished, but again, currently isnt possible. In the end he was happy to remove the preloader altogether, so i was lucky in the end i didnt lose the sponsorship.