Ok I will look into CBWFQ, I'm not too familar with that though. Have any generic examples of config to do this?

Inbound limiting isn't a problem. Outbound they will be pushing large images, so that is where the issue is.

NB: Syntax likely incorrect.

ip access-list extended mytraffic

remark match against your traffic source addresses

permit ip x.x.x.x y.y.y.y any

class-map mytraffic

match access-group mytraffic

class-map theirtraffic

match any

policy-map split5050

class mytraffic

bandwidth remaining percent 50

class theirtraffic

bandwidth remaining percent 50

interface serial #

service-policy outbound split5050

If your still want to limit your bandwidth, even when excess is availble. You could do this.

policy-map restrictbandwidth

class mytraffic

bandwidth remaining percent 50

shape average percent 50

class theirtraffic

bandwidth remaining percent 50

shape average percent 50

interface serial #

service-policy outbound restrictbandwidth