The sleeve launchers as used in combat would work for 1/2A if long grass and no wheels are the issues.

That's a 1/2A combat plane. 

What I was thinking would be along the lines of a rocket launcher guide rail. The ship would not have landing gear as 1/2A size wheels are useless in grass. I envisioned having a PVC platform with a 1/8" length of metal rod paralleling one side. On the wing a section of brass tube would slide over the rod. The PVC support section would hold the model and the rod would keep it from being pulled into one of the side support rods as it accelerated and launched. You would use a pin and eyebolt stooge to secure the ship until ready for release.

Best,   DennisT

Mr. Dennis,
I think your idea is good. Model rocket guide rods are required to be three feet long. I doubt you would need that much length given how well the "carpet release" stooges work. Note that the smaller model rockets use 1/8" rod, and the heavier/bigger ones use 3/16" rod. Those models weigh significantly less.
Would you be doing this strictly for combat, profile scale, or FunFly/sport?
Taking a quick stroll through your idea, I can see a pair of guide tubes attached to the inboard side of a profile fuselage just in front/behind CG. Or a single guide tube attached to the inboard LE/TE, say on a combat plane. My concern would be abrasion of the wing/tube contact surface of the outboard sliding wing. I consider the rod easiest to see around rather than trying to monitor the whole shebang while watching around the PVC tube. It may be prudent to use a PVC pipe of large enough diameter so you could fit pipe insulation or a pool noodle over it.

Mr. Chuck, I "discovered" the drop off gear accidentally. The model was a gift from a gentleman in England. His build log is on RCG in the Control Line forum. When I fly from grass, I lay out four or five 2ft x 3ft pieces of overlapping rubber non-skid floor covering (the diamond textured 1/8" thick stuff). This stuff lays flat as it is heavy enough to matt the grass underneath...but back to the KK Radian. It arrived carefully packed with the gear removed. My first flight was made with the gear wedge inserted in the airframe. Before I made the first half-lap, it vibrated out. I was pleasantly surprised by the "performance change," so I never hard-mounted the gear in the model. I suspect the "socket" will wear out over time, so I do plan on securing it at some point.

Sheep work better in my opinion, although you better be sure you don't have Jimpson weed....

Possibly barring a scale plane, any 1/2-A plane should be able to take off in eight feet or so.

I've used sleeve launchers (good), and cardboard from refrigerator boxes (also good).  If you turn out more horses on the land than it can support, then you can smooth some of the bare dirt and take off from that.

 Cardboard runway is a down and dirty quick solution that works well. I’ve used scrap plywood with good results. As I age, I see the logic of a folding table.