$$$ Reverse remote desktop with holding que?

I have a customer who installs and maintains heating and air conditioning unit for large companies and hospitals. They have a device attached to each unit that they can log into so they can monitor and control the HVAC unit. The problem is that every location is different as far as firewalls and IT. Sometimes it's easy to get someone in IT to setup their firewall so we can access the unit from offsite, but there are time when the IT is not available or has limited knowledge in configuring their firewall.

I would like to know if their is a remote desktop solution that can be installed on a pc at each location that will reverse connect back to our server or workstation that will wait in a que for us to connect. This will always allow us to traverse the firewalls. We have a policy that we would have each customer sign to allow us to make this connection.

Does anyone have any suggestions?

Thanks Very Much!