I rarely block my quilts, but a friend of mine spreads out her quilts, then uses a steam iron. She uses the maximum setting for steam, and then 'hovers' over the quilt, very close, but not actually touching. She then does the same as Nancy: pinning to a carpet that is fitted and doesn't shift, then leaves it to dry completely (sometimes several days). Because she has a couple of quilt-loving cats, she then has to vacuum the quilt because the cats have been all over it whilst it was drying.