Curious as to the application. Some servos and related things like ESC's are not really happy with a much longer pulse frame rate. If we knew how and why you are wanting to do stretch the frame, we might be able to give better advice.
For instance, if you are reading servo pulses from a R/C receiver, and just looking to give yourself more time, you may be creating additional issues. This is relatively easy to do with, say 3 receiver servo pulse streams, if read in order, within the given 20ms pulse window (frame), but exceedingly difficult to do with 6-8. You can even do it without the Servo command (using pulsout instead), as the timing becomes handled by the pulsin reads.
Cheers,
Wreno