Feedback between switching and linear reg. in power supply?

Hello, I make on precision laboratory power supply 0-50V 0-10A.
In first step I use step-down Synchronous Buck converter 1.2- approximately 52V 10A
In second step is very precise linear regulation 0-50V 0-10A.
I have problem how bind switching and linear regulation block so that loss on linear step will minimum. Precisely I search circuit where

Vout – is voltage on output linear regulator input to circuit
Vswout – is voltage on output switching regulator input to circuit
FB – is voltage on feedback the switching regulator, switching regulator regulate Vswout so that on FB =1.2V output from circuit
- If lin.reg is Off Vout=0 then Vswout must be 1.2V and FB too 1.2V
- If lin.reg is open up Vout=X that Vswout=X+0.3 (maybe 0.6V) and FB 1.2V
- Example if Vout is 10V, circuit set FB so that switching regulation set Vswout on 10.3V (optionally 10.6V)

I need a bit advice

Thanks