Controlling the ouput of an Apache sub-request

Hello, I'm looking for a way to run an Apache sub-request and either capturing its output or, if that's not possible, simply deactivating it - which would be fine in my case (although a bit weird in general). virtual() won't let you do this (at least with ob_* functions). I've tried adding a new function to sapi/apache/php_apache.c based on virtual() but without "php_end_ob_buffers(1 TSRMLS_CC); php_header();" but that didn't work : I still couln't control the output from the new function. apache_lookup_uri() can't help because obviously it doesn't go that far (running the sub-request). This can be easily done with an HTTP request but I wish I could do that with an Apache sub-request for increased performance. Has anyone ever managed this ? Thank you