PPTP / L2TP... open connection on specific interface...

…possible without mangle rule?

I basically have X uplinks (currently 2, soon 4) and want to open X pptp connections over the different links to my central server, then bundle them using MPLS / VPLS and bondingto one larger one. Like so many I am stuck with bad connectivity, but can get multiple links. Stupid, yes, but that is it. 6mbit down / 512kbit up is the maximum I can get where I am.

So far the onl thing I can think of is using X addresses on the central location (data center running a Mikrotik 1100AH) then force routing of outgoing packets per IP address in a mangle rule (prerouting mark for the router, then a route attached to this particular mark).

Is there possibly an easier way to do so? One that maybe does not force me to waste ip addresses from my limited public pool?