I don't think there's any logical way to add someone other than instantly - once again due to the memory aspect you will be gone from it if they don't add you immediately whether they win or not.
Lucking out doesn't necessarily mean a BM add. I've added and had people add me due to the fact we ran the same deck (generally not being any popular netdeck) even as the loser.
A lot of requests are BM outright yes. If you don't want to accept because of that then don't, but accepting later does absolutely nothing for those who will BM and is simply a dick move to those who legitimately wanted to add you.