Well, I just did some testing of my own, but I don't think it's possible without specifically redefining F1 in an else-statment.
As soon as F1 is defined as an alias, it stays that way.
HOWEVER, if there are other scripts that use F1 (so not the default help file popping up), you could try using...
alias F1 {
if (%functionkey != F1) { return }
else { myCommand }
}
...but I doubt it'll work.