You might even have to exhaust the quote characters.
Quotes can be tricky.

ALPHA '"c:\program files\other\putty.exe" -load alpha'

(Personally I have PuTTY in my path and I use hotkeys to call putty directly; evars aren't needed IMO since SSH is text-based and so my hands are already at the keyboard)

Just try all combinations wherever you need it, a hotkey, shortcut, etc. one of them is bound to work:

$ALPHA$
'$ALPHA$' (should be same as "$ALPHA$")
!execute [$ALPHA$]
!execute ['$ALPHA$']

That way, you don't have to recall how quotes work.
At the end of the day, whatever works, works.
But kudos if you do remember these sort of things.