[GNC] re-adding billable expenses to an invoice

[Matthew Pounsett]

I accidentally flubbed some keyboard entry while putting together an
invoice and messed up a billable expense item which had been automatically
added when the invoice was created.  Since there is no "Undo" the best
option seemed to be to delete the entry and start over, but I can't find a
way to instruct GnuCash to add billable items to an invoice.  It seems to
do it automatically at invoice creation, and no other way.

Am I missing something?

GnuCash 2.6.21.

Thanks!
   Matt