So I am assuming that
1) you have a PC on your LAN. The PC can only talk to port 80 outgoing via a proxy
2) you have a bamboo server running a cloud service
3) you wish to initiate a connection from the bamboo server to the PC
Don't get your hopes up but this answer https://stackoverflow.com/questions/19161960/connect-with-ssh-through-a-proxy
explains how to use a http proxy to tunnel ssh. Unfortunately most http proxies disallow the CONNECT method
Once you have the ssh to the remote cloud service set up then try it again
with a -R option to allow a reverse tunnel
Then you should be able to connect via the reverse tunnel back to the Lan PC