For calculating due days and discount days for vendors that use net End-Of-Month days, we use the Aged Overdue Payables report, and train data entry people to manually calculate the number of days for a discount on each invoice.

Under the Help menu, you can choose Contact Sage, and 'Send Feedback'. Perhaps if enough additional people send feedback, or 'vote up' one of the previous requests for this feature, Sage will consider adding this.

In the mean time I set up custom reports for groups of vendors that we want to pay on a particular date, and Outlook tasks to remind me to check them. And paper folders for pending payables.