Does any RCX firmware allow a variable to survice shutdown?

I'd like my robot to be able to store a variable, such that when I turn the RCX
off, then back on again, with the start/stop button, the value of the variable
is retained, not wiped.

Is there a third-party firmware or something that allows you to store a variable
in part of the non-volatile memory like this? Since my program is still there on
start-up, and the firmware is still there, I figure there must be some way to
store the value of a variable there too.

I program in NQC, using Bricx Command Centre as the dev tools. I currently use
the Lego firmware 2.0. Is this possible with my current set-up? Is it possible
with any set-up?