We here at DevCentral are the folks who work on the APIs (iControl and iRules). If you have a question about building iControl apps or writing iRules, this is the place for you. As the disclaimer above the forums states: this isn't a place for product technical support. You'll need to talk to the folks in our product support department for questions like these...
With that being said, if the admin guide says it can't be done the odds are it can't (unless it's a added feature that didn't make it into the admin guide - but I don't think so in this case.). I would hop on over to ask.f5.com and see if you can find anything out in the product manuals, solutions, or via the normal support channel.
-Joe
Nimbostratus