if you are going to the DR, I would download from freecruisingguides.com the relevant guides.
Frank elaborates on custom procedures for the US also a bit.
You have to report to the US Coast Guard when you enter US waters. Failure to do so might result in a penalty of 10.000 US $ and probably a lot of other problems.
Whether or not your idea about flying the Q-flag is appropriate (I believe
it is not), I wouldn't run the risk of messing around with the US authorities. I think considering all the international problems they have, they lost
all level of humor
and flexibility. So better follow the rules and avoid problems.
BTW: I believe the Q-flag expresses that you have not yet cleared in and
intend to so in due course. And what would you tell a cost guard guy who might come and visit your boat whilst on anchor