binding a user to a specific WAN facing interface

Hello everybody,

I was asked the following question the other day:
Would it be possible to take a hotspot active user and force him or her to use a specific pppoe-out interface?
A little background:
The location in question is configured as follows. Four WAN connections are bound together to serve the location.

Best regards

1001001

That is possible with Policy Routing. There are a plethora of examples in forums and wiki.