Help with workflow deadlines

[Sherman S. Wright]

Hi -
 
We have a workflow for approval of Purchase Requisition lines, that
currently is set to send a deadline notification after 72 hours.  What
we'd like to do is have it send a notification every 3 days (3, 6, 9,
12, 15, 18, 21, 24, 27, 30, 33, 36, 39, and 42 days) to someone who is
not processing a work item.  Then we'd like the item automatically
rejected if there is no activity (work item not completed) at 45 days.
Anyone have any idea how we could accomplish both of these?  Any help
would be greatly appreciated, since I'm trying to get this done in
development by April 20...
 
Regards,
Sherman