unless your lockout lever is sprung to return to a 'home' position when unlocked your going to need a pull from either side of the lever OR a push, pull system. I doubt a cable could do this tbh, not enough linear rigidity to force back the lever.
what may work is modifying the levers internals (or retrofitting to the top) and spring loading it so it will automatically return to the open position then set up a simple cable pull on a shifter to yank the lever across to the locked position, when you drop off the tension on the shifter, the spring will do the work.
another (easier) option is to have 2 cables running to a pair of brake levers (small 2 finger bmx jobs mounted either side of the stem?) and have a pull from either end. for this to work you will need cable guides either side of the lockout on the fork and it will inevitably look a mess!
could you not flick it over while you are riding? i could reach mine while seated by going under the bars.