LB2120 LTE Modem as Primary

I see a lot of discussion about using the LB2120 to automatically switch to LTE access when the primary internet connection (cable or DSL) fails. "Pass thru" seems to be the key function hers. So far, terrific.  How about the inverse, that is, making the LB2120's LTE access the primary and cable/DSL the fallback when desired (manual intervention, I assume)?