No. In Dual Mode, the H90 behaves like two separate stereo effects processors and cannot be combined or summed.
If you’re up for experimenting, try switching to Insert Mode and putting the algorithms in parallel routing. Next, create a stereo insert and place it before algorithm “B.” Connect one path to I/O 1&2 like normal but connect the other path to inputs 3&4, which are the insert inputs. I imagine, since only the Return of the insert is connected as an input, none of the signal from I/O 1&2 is mixed with the insert effectively giving you two separate paths. Consequently, since the algorithms are in parallel they get summed at the end like you want. Try that.