Marco, I tried posting this to Bax's site but my post remains hidden for "moderation" for now, so I'll elaborate here.
I haven't found any Gemini mirroring the exact "double handshake", so I started by looking for a single "crossed" handshake, which appears uncommon already in itself. Interestingly, these appear to mirror the Roman marriage pose, only with the left figure holding up a finger instead of an item.
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Login to view. --> 15th C Italian (Clm 15743, fol. 100r)
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Login to view. --> 15th C Florentine, two men but same pose. Copy of Hyginus' De Astronomia.
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Login to view. (see image below), another late 15th C copy of Hyginus.
None of these are double handshakes though, and none of them are unambiguously man and woman (it's hard to tell with those clothes). What does intrigue me is that my very limited survey brought up a late 15thC Italian cluster.
Sidenote: the lion in this last MS is drawn in a totally different style than the VM one, but it does have an equally silly face
Edit:
Another 15th C Italian Hyginus. I'm not sure if the "man" on the right has always been a man.
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And another one with a slight variation on the pose:
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Here one or both figures appear to hold an item in their free hand:
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