Hmm... Ever thought of handing them a pen and paper? I know at least some Pokémon are intelligent enough to read and write, though I've never tested it with Tentacools.

[Something to look into, perhaps. It'd make for a fascinating entry in his journal.]

Honestly, though, if it isn't working out, then you could always seek alternatives. Let them choose their mates, perhaps. At least then the choice is theirs.