Seeing the bonsai exhibition at the Bronx Botanical Garden, I have been thinking about constraints. To make the perfect miniature tree, you have to prune the branches, then constraining the ones you keep, with wires.
Is this not like the experiments of OULIPO, the ouvroir de litterature potentielle? there, you might eliminate a letter (say "e," for Georges Perec's La Disparition ) or take some other chosen discipline for your form?
And then think of the possible categories of training: "upright informal" or "slant" or, my favorite, "windswept," attached to a piece of driftwood.. What joyous expanse for the imagination.