While this is true, the OP isn't actually suggesting to sell the codes, he is giving them away free with a purchase of a PC. As that is basically what gift codes are for I don't see that being an issue.

If he was suggesting to give them away with something of lower value, or inflating the value of something to include a cost for the code (£10 for a bar of chocolate and a free game say) then that might look like key reselling.
Plus the problem with most of those keys is not the fact they are being resold so much as the fact they are often bought with stolen credit cards or in other dodgy ways and the end key usually ends up being revoked.

Depends on a game I guess. Old trick with letters cut off from random papers might be safer.

Buying it as a gift code(s) and then printing some sort of certificate with the code(s) on it? I can't imagine that would be a problem with the Terms. The Terms don't specify that the delivery system MUST be email, at least as far as I've read. I remember some way-back threads where people have done so for Christmas gifts and the like, in lieu of having a gOg gift card.

Or maybe I misunderstand your question.

if the person buys from OP then doesn't accept the codes, there is still a chance that the person who bought the stuff could sell it off unless it cant be resend at all after it's been gifted once(i have no idea if this is done already, i haven't looked into GOG TERMS/etc)

i think the better option would be that GOG downloader(i haven't touched yet) if it's a icon on desktop with log in/sign in, you could add a paper that has the account details with it then they just download all the games from there