UPnP through more routers

Situation:
internet-> router A <-LAN-A-> router B <-LAN-B

Router A is doing NAT. When I enable UPnP on it (external interface is going to internet, internal interface is LAN-A), it is working well from LAN-A.

But there is another router B, which is doing simple routing (no NAT). Is it possible to get UPnP working from LAN-B to internet?

Deleted because not related.

Yes Dobby, you are right. I use port forwarding for some applications, but it would be great if user could use any UPnP application without my intervention.

Deleted because not related.

Deleted because not related.