use feature doesn't add given. It simply allows it to be used. It's as ingrained into Perl as the addition operator.

Using source filters, it's possible to change Perl's grammar. That's what Switch does, which is probably the closest there is to 5.10's switch in older versions.

However, Switch introduces impossible to debug problems when its source filter doesn't correctly parse the Perl source, and the syntax and semantics are different than 5.10's.

I strongly advise you to avoid using it. Upgrade to 5.10 or tough without given.