When there is a harp glissando that is not covered by the sampled ones, you can time stretch it - something I never tried - or  program the individual notes without too much difficulty.  When I've done that I doubled the notes that would be enharmonics given the pedal settings of the harp, and that makes it sound very natural, especially if you use some humanize in the timing and velocity.   This is also how you would program a glissando in an unusual (but possible for harp) scale.  

I never tried the time stretch for this, interesting. Another option, and the most common I use in these cases, is simply to to play a gliss on your keyboard from the starting to end note, practice a few times timing it, and then add the appropriate accidentals in the piano roll. I also repeat some notes to make it more realistic.

Shouldn't it be possible for VSL or a third party to create a plug-in that would transpose each of the seven white keys in each octave either up or down a semi-tone? That would allow us to play glissandi just as we want them in real time. Please advise!!!!

Thanks for this response. I know of Dorico's capability in this area. I prefer to work in Cubase, and hope that Steinberg augments their MIDI input transformer to include harp pedaling emulation.