HowTo shadow someones RDP to a remote 2008R2 Server session

HowTo shadow someones RDP to a remote 2008R2 Server session

So If there is 3 computers involved:

1. nodeA the remote contractor's computer (Win7:controlling)
   
2. nodeB my local network workstation on separate subnet (Win7:watching)
   
3. nodeC server both wish to share connection for (being worked on/ sharing out to both other nodes) (Win2008R2)
   

How do i let nodeA connect to nodeC and then nodeB laters finds and (transparently as possible) joins that active session and just watches; even records if possible.

thanks