Hi I've the hpro 2009 and, just as info, even with the airush razor you can have the 6 line mode.
First. the oh shit handles on the side work fine, you just grab one and let it go the bar (without release the safety if you don't want to lose the CL).
Second. I've the 2011 bar which as a longer throw and you can modify the 2009 bar to have the depower throw longer. I remember that with the 2009 bar I was always full on and it wasn't so nice.
To modify the depower throw length just undo the knots from the bottom of the trim and redo it with more rope. Be sure to check that the knots on the pigtails at the V above the trim are lowered (as you want have more depower not less!)
About safety you can try several things
remount the 5th line on the bar and check (with full powered trim) that it has the same length (or a couple of cm more) than the front. Attach the 5th line to one front pigtail on the kite.
Make other 2 bridles like the one that are on the kite and use at the same time 6 line and 5th line. you are going to have advantages on the relaunch and all the usual advantages of the 5th line. But could be that you are going to spend more time to rig your kite.
try to made a double depower setup like here http://www.wainmanhawaii.com/carrot-bar/setup#default
You are not going to have full depower releasing the safety but it's not going to be bad. You need a good bungee like this http://www.kitesurfing-shop.co.uk/buy/a
... gee-149446 otherwise check in a nautical shop. Just be sure about the breaking point and the diameter otherwise wont pass in the small hole on the bar. THIS IS NOT A FLAG OUT!
If you're going to use the 3rd method be sure to change to a long depower throw in order to maximize the effect. In my opinion 10-15 cm more of depower throw (and so 10-15 cm less on the V above the trim) could be a good compromise.
The second method will be the one i'm going to use cos I prefer be sure to have a proper safety. Even if some one can claim you are using a sle rather than a pure C but who cares?
The first method is the ugliest of the three but at the same time is the easiest to set up.
Have a lot of fun!
Cheers for the detailed answere, I'm gunna set up the second option. I'll need to get some extra line but apart from that it should be fairly simple.