upload queue for multiple interfaces ?

I have 4 vlan tagged interfaces under eth5, vlan1…4

I have 3 wan links, wan1, wan2, wan3.
I want vlan1 use wan1, vlan2 use wan2, and vlan3,4 use wan3.

I know how to create down/up queues for single interface,
wan1 - vlan1
wan2 - vlan2

When creating a tree queue there is only one interface parent possbile.
however I would like the up/down traffic from vlan3,4 use wan3
wan3 - vlan3,4

What is the trick ?
should I bridge the vlan3,4 then use bridge as the parent to upload queue ?

Would the bridge not pass traffic between 3 and 4 ? as I want them isolated from each other.