If you could use a lower CPU intensive crypt like blowfish, it would be easier.
Are all these trading partners in different locations or are there semi large groups in the same locations?
all these are end users. they connect software from home / offices.
Maybe a hundred or so share an office, you could set up IPSec tunnels to each remote office and pass all 100 through that tunnel. It takes a lot less CPU to pass 100 combined then 100 separate connections.