There is no way to do integrate Version Control Systems like VSS into the Forms Builder if you expect it to work in the fashion of Visual Studio.
I am not really familiar with VSS; however I guess there is a external client for it which you surely can use.
I am curious: do you have a existing Repository with VSS in place?
VSS isn't actively developed anymore; if you are already on VSS you should take a look at it's successor Team Foundation Server (pretty sure there is an upgrade path).
If you are in the progress of initially creating a repository for your project I seriously would think about if VSS is the way to go, as it will be desupported 2017 and you don't want to end up with a desupported Version Control System. I'd even think about if a Microsoft Version Control System is the tool of choice; it may work very well with their own Development Tools but might not work as well with other tools, leaving aside you bind yourself to Windows and Windows alone as far as the Server goes (not sure about the Client).
As for now we are using Subversion for 6 years; as for now we have a lot of different projects hosted on our Subversion Server; from Forms to Java, C/C++, python, Visual Basic and some other things. We never regretted the decision to use Subversion.