Não, mas você pode usar um RewriteMap e ter suas variáveis processadas por um programa externo:
MapType: prg, MapSource: Unix filesystem path to valid regular file
Here the source is a program, not a map file. To create it you can use a language of your choice, but the result has to be an executable program (either object-code or a script with the magic cookie trick '#!/path/to/interpreter' as the first line).
This program is started once, when the Apache server is started, and then communicates with the rewriting engine via its stdin and stdout file-handles. For each map-function lookup it will receive the key to lookup as a newline-terminated string on stdin. It then has to give back the looked-up value as a newline-terminated string on stdout or the four-character string ''NULL'' if it fails (i.e., there is no corresponding value for the given key). A trivial program which will implement a 1:1 map (i.e., key == value) could be:
#!/usr/bin/perl $| = 1; while (<STDIN>) { # ...put here any transformations or lookups... print $_; }