I have a 22" pushrod to a MK bellcrank in my MATRIX with no support and
it works fine. I used a 1/4" rod from the servo to the bellcrank and 3/16" rods
from the bellcrank to the elevators.
I am scratch building a new plane which will require a 29" push rod and I boxed in
a 1/4" CF pushrod with 1/16" balsa. Just CA'd the balsa strips around the push rod
the full length almost to the threaded inserts and it stiffened it up considerately.
Didn't add hardly any weight and it just looks like a square balsa pushrod now.

tommy s