I'm not necessarily suggesting you do this, but if your variables are, say, $name, $email, etc. (i.e. they aren't in hashes) you can use symbolic references:

s/<!--var (\w+)-->/${"main::$1"}/eg
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(so <!--var foo--> would be replaced by the contents of $foo.)

The only real advantage to punk music is that nobody can whistle it.