So this basically just popped into my head. If people are interested, I'll take it further. If not (barring any more persistent inspiration) I'll let it be. Thanks and hope you enjoy it!
Dear Mr Severus Snape (Order of Merlin, First Class),
I don't know how well this will work, but I reckoned it was worth a try.
It has recently come to my attention (by way of a highly disturbing accidental pensieve trip) that I have you to thank for my existence. Turns out that my grandfather, in addition to being a bit of a tosser, was also a bit of a prude. Gran was apparently his first. From what I've heard of you, seemed you'd get a good chuckle out of this and, given with the chance to toss this beyond the veil, I found I couldn't help myself.
Doubtless I'll never get a response even if you do receive this, so I'll just cross my fingers and hope my Gramps doesn't get it by mistake.
Albus Severus Potter.