So for little more reason than, 'to see if I could', I was trying to get Blue Prism's C# to be an IronPython interpreter:
http://www.secretgeek.net/host_ironpython
In trying to make it work ( which I did eventually, but that's neither here nor there) I found out that I could get .NET 4.0 in code stages in Blue Prism's objects.
Looking for help with IronPython's .NET 4.0-ness I stumbled upon this MSDN article/property:
https://msdn.microsoft.com/en-us/library/w4atty68(v=vs.110).aspx
detailing the property. I looked for an app config in the default Blue Prism folder, and on a whim, added in this bit to the Automate.exe.config file, within the tags, just below the tags:
When I restarted Blue Prism, opened an existing object, created a code stage, and put in some valid .NET 4.0 C# code I found that it compiled and worked just fine. Oh keyword 'var', how I missed you.