Thanks for the suggestion. Unfortunately this is not very easy to do.
As it is, withdrawals are done with the
[wallets_withdraw] shortcode, and intra-user transfers are done with the
[wallets_move] shortcode, which will be improved soon at the upcoming 3.0.0 release. If a user attempts to withdraw to a deposit address of the same system, the plugin performs in the backend an internal transfer (aka move) instead. The frontend has no way to know which addresses belong to different users.
I would suggest that you use your page’s text to inform users about this. You could encourage them to use internal transfers or otherwise notify them that if they are sending to a deposit address to another user on the same site, no blockchain transaction will occur.