Meanwhile I've knocked out a VST MIDI Plugin that does the job and turns any synth into a mono monster. I must say this makes a huge difference in my articulation possibilities, the effects range from rounded note transitions over hammering-ons and -offs to huge slides depending on the settings. These effects are the salt in the soup for flowing, moving solos and typical for the sound of many natural instruments.
All these effects are simply controlled with my breath: I start a new note with a 'T', this stops the air flow for a short moment and provides enough pressure for the new note. The result is the usual staccato sound. But when I move then to another note without stopping the air flow, no new note is triggered, instead the synth glides to the new note without a pause or retriggering. This works on the harmonica even for one-note transitions with a quick chance of the breath direction.
I strongly suggest to add this feature to the monophonic mode of the DM48X. The logic behind it is quite simple: Delay all MIDI note-offs for some milliseconds. That's enough to provide overlapping note-ons und note-offs needed to trigger the glide feature of many professional synthesizers.