We have a great community hempy thread here on RIU
World of Hempy
.... Lots of peeps with successful grows and we try to answer all Hempy related questions.
I'm guessing you require the cubes for cloning. .. possibly for more than a couple at a time? .. Have you considered building a 'DIY' aero cloner. .. Its what I use and works great.
other options for cloning would be the peat pellets as suggested. or even placing the cuttings into individual solo cups filled with a Perl/verm mix and then under a dome.
Good luck.