  We compute the fully-differential B -> X_u l nu decay width to all orders in
perturbation theory in the large-beta0 limit. Each of the five structure
functions that build the hadronic tensor is expressed as a Borel integral,
summing up O(CF beta0^{n-1} alpha_s^n) corrections for any n. We derive
analytic expressions for the Borel transforms of both real and virtual diagrams
with a single dressed gluon, and perform an all-order infrared subtraction,
where the Borel parameter serves also as an infrared regulator. Expanding the
result we recover the known triple-differential NLO coefficient, and obtain an
explicit expression for the O(CF beta0 alpha_s^2) triple-differential NNLO
correction. This result can be used to improve the determination of |V_{ub}|
from inclusive B -> X_u l nu measurements at the B factories with a variety of
kinematic cuts.
