I keep mine permantly engaged, and I know several other members here do as well or at least reverse the action of the cable so the default position is engaged and then you would squeeze the lever to disengage. It's pretty simple to lock the cable at the adjuster on the gearbox. I use a brake cable anchor and press it against the adjuster and then pull the cable by hand and tighten the anchor then cut off the excess cable. (See photo below) I've also gone to the trouble of reversing the action of the two springs on the engager arm so they[ are pressing the two couplers together instead of pulling them apart. This way if the cable anchor slipped for some reason the engager will stay engaged. Another thing I've done with my gearboxes is weld up the 11t freewheel.
ocscully