PHP considers all require/include files to be plain text, and will treat them as such until it spots either the <? (shorttag), <?php (regular tag), or <% (ASP tag) character sequences in the stream, after which it switches into PHP mode, until it hits the end of the script or the corresponding closing tag (?>, %>). As such, there's no way to have PHP treat a compiled input as program code. Even an EVAL won't help, since that just invokes the same parser that didn't trigger off the binary input in the first place.
BZipped code itself isn't executable either, unless it's been wrapped by an auto-extractor stub.
Since it would appear to be BZipped, why not try un-bzipping the file and see what you get? Maybe the class file was downloaded as a .bz2 distribution and simply got renamed. The uncompressed copy may contain the appropriate wrappers to allow execution.