You can take root cuttings. You will of course have to lift the parent plant. Select a couple of thick (pencil thick if possible) roots and cut off a decent length. Section the roots to about 2inch lengths and lay them horizontally on a seed tray full of seed compost with a little extra grit. Cover them with same depth as their thickness and keep moist and cool either under greenhouse staging out of the direct sun or outside (again out of direct sun). The cut ends should callous over and produce new bud tissue within a few weeks.