Well there is something that can be done with the VERSION_INFORMATION file but it's quite the procedure. I'm trying to figure out a way to write software to automate the process but here's basically how it works:
Unzip a MER with 7zip.
Open a the VERSION_INFORMATION file with Notepad++
Use it's converter plugin to convert the text from ASCII -> HEX
This will reveal the following:
030720 = V7
03060A = V6.10
030620 = V6.0
0305 = V5.10
030520 = V5.0
030420 = V4
Didn't try < v4 but I'm sure that there's a pattern here...
If I can figure it out, my hope is to make a small executable that you can just point at a MER and have it do the above work for you to report the version. Or maybe there's an easier way, we'll see...