Explicit Supply - Supply Unit Movement Question

[Radetzky]

dear sirs

i'm looking for a way to pre-plan the movement of SINGLE supply
units when 'explicit supply' is activated. playing a full campaign on
a large map tends to turn supply movement into a logistic night-
mare and it seems one can only give AI movement orders to the
whole supply corps formation. but you don't want all of your supply
trucks to huddle around a single hex, do you?

so, any ideas on this one?