thanks for asking.

I'm afraid I can't offer you help with that specific problem, though. 
There does not seem to be a way to do this via AppleScript and I 
don't know of key combinations that would safely achieve what you 
want to do, either.

If all you need is the Select All, though, you can do the following:

1) Go to the mapping settings for iTunes 
2) Click on the entry for the button you want to map to the Select All. 
3) Select "Custom Actions". 
4) Enter the data for Select All (Apple + A).

Hope that helps.

Best regards, 
Felix