My question or more so a issue.

In an environment where one machine runs Windows XP and has access to the internet but is restricted due to a work environment and runs .NET 3.5

Whilst the other runs Windows 7 and runs .NET 4.5 and still restricted.

Running or adding the .NET to the setup is not available since running any updates is restricted, I found myself not being able to update the client through the internet due to restrictions on a certain port blocked.

The Issue:

When I go to deploy the application I have to create 2 builds, one for the Windows 7 and the other for XP. Is there a way for me to deploy these so I dont have to go back and forth. If Windows 7 has 4.5 surely it would just run the .NET 3.5 application, is there an easier method to this madness of mine?