See the attached software SYX files version 2.6.5.
This adds extended parameter 47 (P2 47).
When P2 47 is set to 0 both the first and second modulators work in additive mode. That is, they both modulation.
When P2 47 is set to 1 the second modulator is used to attenuate the depth of influence of the first modulator.
Attached is an example patch that shows how the second modulator attenuates the first.
I've been meaning to do this for a long time. I finally got enough free time to do it - woohoo!
Enjoy!