  A precision method for determining |Vub| using the full range in q^2 of B->
pi \ell nu data is presented. At large q^2 the form factor is taken from
unquenched lattice QCD, at q^2=0 we impose a model independent constraint
obtained from B-> pi pi using the soft-collinear effective theory, and the
shape is constrained using QCD dispersion relations. We find |Vub| =(3.54\pm
0.17\pm 0.44) x 10^{-3}. With 5% experimental error and 12% theory error, this
is competitive with inclusive methods. Theory error is dominated by the input
points, with negligible uncertainty from the dispersion relations.
