You can manually create an expense and mark it as unpaid and add a due date. This will show up as future expenses on your Cash Flow and also show up under Bills Due on your Dashboard's Spending Stats.

To do this, go to your Transactions dashboard and add an expense. Click on Paid Date next to the date, and you will notice it switch to Due Date. Feel free to change the date to the actual due date. Once it's paid, click Due Date to switch it back to Paid Date.

If you have your data auto-importing from your financial accounts, this may result in duplicates. Be sure to delete one of the paid expenses to avoid inaccurate reporting. You can also create these in a manual bank account that you have to NOT report to your Profit & Loss, then once a month go through and mark them as paid as soon as they clear your bank account.