Getting "random" MAC addresses on VPN Clients (OpenVPN or L2TP)

How can I control the MAC that the Peplink VPN server will use(maybe use the client’s VPN adapter MAC)?
Without it, I lose much of my network controllability (eg. assigning static IPs).

I’ve tried all sorts of things with OpenVPN, L2TP and even PPTP. Nothing helps.

Aside: I want split-tunnel, which is working for both OpenVPN and L2TP with Windows.
Android, nope - but I believe that’s an android issue.