if you want to do a double spend, you will have to wait until the transaction drops out of most miners' memory pool. wait a few days, do the forget tx with pywallet, and resend the transaction.
Do you think mining pools are holding the transaction for days -- and thus rejecting conflicts -- even though they're not willing to include it in blocks?
That would seem to be a waste, if there's zero chance of including it (as opposed to just waiting for block space, which because of many recent undersized blocks doesn't seem to be the issue).