Since you've already unlocked your bootloader, you should be able to flash a recovery from fastboot and then use that to root. This will get you root on your stock ROM (but not S-OFF):
- Download ClockworkMod recovery for the doubleshot from this link
- Download the Superuser/su zip file from this link
- Reboot into fastboot mode. To do this, remove power off the phone, remove the battery, then hold volume down while you re-insert the battery and press power. When the bootloader menu appears, press power again to select "Fastboot".
- Flash the custom recovery image:
fastboot flash recovery /path/to/clockworkmod.img. - Reboot into recovery (reboot and hold volume down, I believe, otherwise use 3#3 above to boot into the bootloader then press volume down to select "Recovery" and press the power button).
- Copy the Superuser/su zip file onto your device and install it from recovery. It may be easier to get the zip onto your device if you first reboot normally and then use AndroidsAndroid's mass storage feature to just copy it over.