When you mean bath, do you mean dump the keys in bucket with the solution and shake it around? or wet a microfiber cloth with a mixture of Simple Green and wipe them across the keys, 1 at a time?
I've done a simple mixture of simple green 1:1 on surface keys, and it works out quite well. For key grime that was stuck in deep any my towel couldn't reach, I dumped those keys with a mixture of denture cleaning tablets (I remember reading someplace here as that was what a member recommended) for ~10 minutes and then rinsing them in clean water after they are done "fizzing."
Denture tablets were cheap, $3 USD for like 40 tablets, I recall.