Safest way to play it
The safest way would be in the smallest increments possible. Any regular bet. Usually I'd rather Come, but sometimes it's more satisfying when you Don't Come and let somebody else do it. Every time you win, you have to pull the live chip back and replay the non-cashable one. Using this method, as your betting increment approaches zero, your return should approach EV, which I recall is around 99% for that game. Not bad for a 10% bonus.
The other matter is that as your betting unit approaches zero, your time spent playing your bonus chips will approach infinity! So you have to calculate: the value of your time, the expected length of a hand of craps, and how much additional risk you are willing to accept in exchange for finishing this mission quicker and going to do something else. That's your homework assignment, don't ask me to grade it, it's been forever since I've done that stuff!
