generic SNMP check: need --format-custom in --config-json mode

I need to monitor several values, which I want to have in a single graph.
Unfortuantely, I need to do some math on each value (/10 for some and /100 for others).
When I grab a single oid, I can do that with --format-custom. But in --config-json mode, format-custom does not do anything.
Can these options be added to the --config-json mode?

BR
Horst