Bob
Short answer is NO .. it is NOT POSSIBLE.
The iTouch and iPhone are quite different from the old iPods which you could switch into disk-mode and easily use as external USB drives. There is NO way to do this with iTouches or iPhones legally anyway ... with one exception if you hack/unlock them.
If you use one of these unlocking tools you will gain access to the underlying operating system and hard drive on the iTouch and can copy over any data you wish. Unfortunately this is against the Apple-way and they provide no support or warranty once the iTouch has been unlocked. Then again there are thousands of users who have done it in order to add 3rd party applications and other data to the iTouch and iPhone.
A quick search in Google will reveal a number of tools to do this. Make sure you select the correct one for the OS version on your iTouch.