Depending on the surface you're flying from the results may be either disappointing or look really goofy.

One or more 2 foot by 4 foot sections of plywood, laid out along your line of flight, should be enough to get off the ground, unless you've got a really wimpy engine.  When I was growing up I had one with a stooge built in, for self-contained launches from the neighbor's horse pasture.

Or launch from a sleeve.

The control line circle I fly from is a bumpy corner of an RC field that the club started mowing when we realized that a couple of folks wanted to get back into CL (it helped that the guy who usually mows is one of us).  Since it's bumpy it has scalped spots and deep spots.  It's hell to practice a smooth take off with a regular sized stunter, but there's scalped spots that work quite well for an 049 powered plane.

Which is the long way of suggesting that you get out there with a weed wacker and scalp a runway for yourself.

You can make a nifty runway from all those political signs that are about to go in the dumpster.  These are the plastic ones.   

They generally are 2ft x 1.5ft.  You trim an angle into both short sides and hinge them together accordion style with duct tape.  4 will make an 8' runway that folds up to 1" thick!

To calculate the angle:  angle in degrees= 114.6/line length in ft.   So for 45' lines you get 2.5degrees. 

If I could find some I'd grab them. Problem is I never see any to take.

The signs are all over around here for weeks after the election.  I parked at one mini-mall and picked up 6 from just one corner.  There were similar amounts on the other 3 corners, but enough is enough!

on the contrary, I love cutting up the opponents' signs for planes!