Actually no - even that has problems. First, you need to be able to introduce a compiler. Of course this doesn't need to be the production environment but there is still a change control process that must be adhered to. The next problem you will face is that compiling C extensions for Perl using a compiler other than the one that compiled Perl usually doesn't work. This means either recompiling Perl or creating a stand alone executable and using system calls. These both have the same problems. Keep in mind that I fully recognize that these hurdles are not technical and are quite silly but one has to choose what they want to spend their time doing.
"I need to very quickly compress these strings into the smallest space possible and also be able to expand them back again later as quickly as possible."
"My environment ... no compiler"
No mention of change control or process there - you wanted raw speed and little space used and you couldn't compile on the production machine.
But I can imagine the approach I was thinking of - spawning an external process - (and the communication with that process) would negate any speed advantages and I'm too lazy to prove it one way or another so I'll shut up and go away!