basically it can be done ... but will be slow ...
http://code.google.com/p/hxformat/
actually you would load the string and then it'll be decoded into an Array of bytes (using Bytes.ofString) ... this will take a lot of time ... and you will not be able to do a lot with the results, i guess, since AS2 api is very limited ...
you will need haXe, which is an open source language, that allows you to target lots of platforms, one of which is AVM1 ... just go to haXe.org ... and find a suitable IDE to get things compiled ...
problem is, it will be easy compiling the code, but you may have a hard time using the outcome, since haXe->swc only works for AVM2 ... but there are multiple solutions for that ...
anyway ... if possible, you should port your code to AS3, as fenomas suggested ... AS2 is really outdated, poorer as language and target's a slower VM and a much smaller API ... also, there is a lot more AS3 libs out there ... just my personal opinion ...
well, good luck anyway ... ;)