You can do that.
I have inherited a circuit where it appears that the LTC3122 sometimes fails to shutdown fully (< 1uA) when the SD input is held low and instead continues to consume ~65uA.
In the screen shot below:-
Can you comment on why you are looking for a buck-boost converter for this application? Typically buck-boost converters are used in applications where the input voltage varies above and below the regulated output voltage. In your application it appears…