Store a setting in background process?

I have made a watch face that get data in background and shows it on the watch face. 
There is two ways to get the data and I try a way the first time and if that gets an error I try the other way.

How can I store what way that is preferred in the background process?  

I cant use application storage (not allowed to write from the background process apparently) 

The setting would only be used in the background process.