Core strength exercises are my way of dealing with this.
I used my tri-bars for about 150km of the London->Edinburgh ride I've just done (mainly following the LEL route). Very useful for bludgeoning my way through a headwind, or taking it easy (same speed for less effort, or 2kph faster for no extra effort). Definitely a good idea. Had them on the bike for ages and use them whenever possible. A 10 second break and stretch is enough every 10 minutes or so. My longest stretch on them was probably 2 hours or so of dull Cambridgeshire.
Remember that you don't want a full on TT position on aero-bars for long distance. You want a comfortable crouched position that you can hold for long periods.
Pic 1:
http://www.greenbank.org/bikes/tempo/tempo7.jpgIn use Oop North:
http://www.greenbank.org/misc/le13.jpgThey're Profile Century Aero ZB tri-bars mounted on Profile T2 Wing bullhorns. TRP RL970 aero brake levers.
GPS goes on its mounting at the top of the aero bars (easily visible in both aero-tuck and normal position) but you'll need "closed" tri-bars to do this. Rixen & Kaul MiniMap mounted on one arm of the tri-bars. Don't use this when using a GPS.
Computer will be moved to the stem when I get a chance and that Minoura Space Grip will be removed. That's just the way I had it setup before I swapped the handlebars.
The other (forward) space grip holds the light(s). Right now it's got Solidlights on it, but for LEL I'll be using two B&M Ixon IQ battery powered lights and getting rid of the extra drag of a SON wheel (no matter how small the drag is).
I don't have to worry about covering the gears or brakes as I don't have any gear levers and always have two feet on the brakes.