I have not tried this and I can not guarantee it will work and won't brick your phone.
You also will not be able to back up your WiMax keys this way.
If you are still determined to try...
You can try downloading this
to your phone.
Download root explorer from the market(paid app) go into the SD Card folder, then the download folder. Locate the zip, then long press and select move, make sure you are in the SD card folder, but no sub folder and paste.
The reboot into bootloader by turning your phone off. Then turn back on while holding the volume down.
I haven't done it myself, but you should now be prompted to reboot after the recovery zip is flashed from the bootloader.