Sustain pedal for external instruments

I just bought Behringer’s fine Model D and Pro-1 synths.
Unfortunately they don’t support sustain pedal out of the box, and while it’s a no problem with a mono synth, it’s a tad annoying when using a MIDI arpeggiator, for instance.

Is there any way within Cubase 10.5 to direct the sustain pedal CC to them?

If they have input, then you send the CC on that port.

There’s your answer – if the synths don’t response to CC 64, i.e. the manufacturer hasn’t implemented the feature, then there’s nothing any software can do.