There is a program called FPS Patch that does this. Written by the guys over at yoku. The last patch broke the program, unfortunately. I got them to update it once before but they've been somewhat unresponsive this time around. The link to the forum post is here if you'd like to go request an update there as well.
http://forum.yoko.com.ua/viewtopic.php?f=12&t=17367
Just as note, this Patch can be detected very easy. Once the Checksum is different, its pretty easy to detect that its a modded client.
After testing this with older clients on freeservers (and unpacking and sifting through the whatever stream on execution with a sandboxed winxp) I don't know if this is correct now.. It's injection and that shouldn't modify the executable's checksum... However what I suspected, and verified through about 5 minutes of research on yoko forums, is that the packet stream will become awkward in regards to mounted vs unmounted players from the client to the server, this was an issue posted back in like 2011 or something though, before this individual fps patch was produced and it was more of a work in progress feature for the yoko injection application as a whole.
I could be wrong though, it's just what I think make sense. Injection as I understand is something that bypasses hardcoded client modifications and such checksum detections via live manipulation of the client's memory resources.