i think the most simple thing really is to create a C# client that'll embed an SWF for communication purpose ... communication between C# and SWF can be done easily through local connections ...
otherwise, you will be having a hard time ... i summarized how flash p2p works in a related question ... there is an awful lot of net-code you will be having to write (starting with the whole protocols that stratus alone uses, and then reimplementing the whole p2p protocol based on UDP, which secures data much like TCP does, and should not be a twoliner) ... i'm not saying it is not feasible ... but it seems unneccessarily uncomplicated ...