Is there any (known) way to have Arxiv waive the endorsement requirement?
Just to check, your first request for endorsement emails were hopefully to your thesis advisor/postdoc advisor. If they haven't gotten back to you, either you definitely haven't waited long enough or there may be some other issue (they don't want you to submit to arxiv without them looking at it first?).
Worth looking to see if there are other ways to get a .edu address. If you are a researcher in a relevant industry, you could potentially get some degree of honorary affiliation with a local university just by asking the right people. However, this is probably much harder than getting an endorser! You should also look into your PhD and undergraduate school's policies: many offer "alumni" email addresses that are .edu - but I'm not sure if this is sufficient for arxiv's purposes.