[Asiaplay]

Then will not work - you are right...

Only thing can think of is use stock anyway - and then hide the quantities box so they always buy one only.
Then set maximum order per time in settings to ONE and set quantity in stock for items you want to sell to 1,000,000 (high number, so they never stock out) and those want to hide to ZERO.

Know is a work-a-round - it might just be easier to get someone to code a tick box next to the variant combinations screen, so that you can turn some variants off... pm me if you want a link to a competitive programmer which we have used for a long time now (my own coding ability is not good enough to do that unfortunately - so can not just tell you the code).
But that should be an easy mod to get done.

Cheers - Asiaplay

PS: just check if you can set a variant to not show i.e. that the function to tick, do not show a variant... does not exist already on the variants screen, in latest version (guess it doesn't - but not 100% sure, as we don't use the V4.2.X and later versions yet).

Cheers - Asiaplay