If your bootloader is not unlocked already, you will need to unlock the bootloader in order to flash the ClockWorkMod recovery. Unlocking the bootloader wipes the device. So as far as I know, that won't be an option for you.
Perhaps you have seen this toolkit to root the Nexus. It looks promising, but I would bet it won't work without USB debugging / ADB enabled. It may be worth a shot anyway. If it doesn't work, you will still be in the same boat.
Alternatively, you could just keep trying lock screen patterns. Hopefully muscle memory will kick in.
To use the toolkit, you need to know your build number. See this thread for some info that might helph you figure out what your's is. If you can't narrow it down enough, you might be able to use the
Android *.*.* Any Build option for your carrier. Since you mentioned Jelly Bean, we can assume the build will be
4.1.* This doesn't give you the exact one you need, but it will help some. Based on the FAQs for the toolkit, it looks like you should be able to use the
Android *.*.* Any Build, but you must select the right version for your carrier. If you want more info on this, post your carrier and region (US, Korea, etc.) and we can probably narrow things down a little more.