Wire mobile radio into car speakers?

I have a GMRS radio in my vehicle for off roading. I was wondering if there was an easy solution to wiring it to a speaker (not the aux radio input). I know I can get an external speaker but I wanted to see if there was an easy solution for this first.

I did not see an easy solution or write up besides people talking about buying external speakers. My idea is to get a cheap audio switcher that lets me take 2 input to 1 output and 3M sticky it under the seat. Then wire the two radios as inputs.

Easier way to do this? Just a bad idea?