Boss FS-5U control pedals and Quad Cortex

In the past I have used some extra (footswitch) control pedals for my older modellers: 2xBoss-FS-5U with a TS/TS->TRS Y-cable to a TRS input.
Now with the QC I use a Mission Engineering SP1-ND-GY, so one expression pedal and one foot switch.

I was wondering if the 2 FS-5U can be used instead of the foot switch on the Mission pedal, and so that I have 2 extra foot switches instead of one (could be a problem assigning?).

Anyone that tried something like this? Is it safe? Should I contact support?

Thanks in advance