I haven't rooted these, but I found some info to help you:
"Whatever you decide, propagate every year from the new growth at the base of these evergreen euphorbias. Carefully cut some of the new growth (avoiding contact with the harmful sap) and trim back to 4in in length - removing the bottom 2in of leaves. Fill a 3in pot with a mixture of 50 per cent sand and 50 per cent compost and immerse one cutting in each pot. Leave in a cold frame or a shady place until the following spring, then plant the well-rooted cutting outside. If the cutting hasn't rooted, leave it until autumn."
I also read to dip the end of the cutting in charcoal.
