I don't think there's any way around it, any vasodilating drug can dilate the blood vessels in the brains convering and cause pain.
I rememberthe headache well from the "poppers" of yore (inhaled nitrites) when they were the only sexual enhancing drug around.
Even Viagra, which I didn't much care for gave me that "certain" headache.
Probably some sort of vasoconsticting drug would work after orgasm, but that sounds like VERY risky business.
I guess we just add headache pain to the $10 price tag and do a cost/benefit analysis