Click here for a website about the Rhubarb triangle and how they force rhubarb there.
If someone asks you for an offset of rhubarb, of course you don't have to lift the whole clump, you can nudge off a section from the outside. Refill the hole afterwards with a rich mix of soil and manure.
FORCING RHUBARB OUTDOORS
You can force rhubarb outdoors for an earlier, more delicate crop, with very little extra work. The pretty terracotta rhubarb forcers you see in the poncy gardening mags are NO USE FOR THIS AT ALL - rhubarb grows much taller and takes up more space. An old dustbin with the bottom taken out, or one of those similarly shaped plastic compost bins, is a much better bet. Place the lid on not-quite-straight so you get some ventilation. The sun will warm the plastic and bring on an early harvest.
Don't force the same clump every year. You can have two ot three clumps so you can force clumps in turn, giving each one at least a year to recover.