Your best bet is GPS and the heliroute maps and mark off as you go along, have a pasenger that can read maps.
The most likely issue is that your nicely planned route can't be flown due to other traffic or changes in runways and then you'll suddenly have to do a lot of thinking on the hoof so make sure when you plan your route you consider the other ways you may be taken.
Ideally try and take somebody who has done it before, or even better, be a passenger with them whilst they fly it so you have more time to think about where you are any what's happening prior to doing it yourself.