Strictly speaking its not important, what the structure is. The only thing, that matter, is stack sizes relative to the current blinds of you and everyone behind, and opponent tendencies. In
freerolls in general you can expect some looser action, which mean, you should reduce
bluffing to a minimum and widen your value range.
It can also make a ton of sense to open very large or even open jam strong
hands, if people are still going to call with worse. I have seen people open jam aces for 100BB in a freeroll and still get called by all sorts of hands. Maybe you dont need to take it that far, but you dont have to stick to default sizes like 3BB either, if people are going to call much larger raises as well.
When stacks get very short relative to the blinds and antes, which will invariably happen in such a fast structure, you have to get it in extremely wide. Sometimes even the antes might be more than your stack, and then you obviously can not afford to fold and wait for better hands very often.