It did not seem like I would get any help with this so I made a quick hack:
sregPath = "SOFTWARE\Classes\Paint.NET.1\shell\edit\command"
Set oRegistry = GetObject("winmgmts:root\default:StdRegProv")
If oRegistry.GetStringValue(HKEY_LOCAL_MACHINE, sregPath, "", sString) = 0 Then
sString = Mid(sString, 2, Len(sString) - 7)
Call RunWinApp(sString, sPath)
Else
sString = "MSPaint"
Call RunWinApp(sString, sPath)
End If