Essentially a 1/2" diameter, stiff, multi segment tent pole, will do,
just make it long enough.

parts : 2 diameters of aluminum tubing one that fits inside the other.
some elastic cord, and a couple caps, for the ends,
that will also hold the ends, Of the elastic cord.

I found a ball knob that goes over a knot in a loop of elastic cord.

I use it to hold my front brake, to lock the bike to a pole, so it wont fall over.
how tight depends on where you tie the knot.