Hi Dave,
To do this, I recommend filtering out all of the estimates with a status of "draft" from the grid on the ContactsPortal_Home screen. Since this is a default screen you can't edit it directly, but you can make a copy, and then replace the original screen with the copy. To do this, edit the grid on the screen DueTransactions. Skip to step 3 to setup the filter. You should see 3 filters already there, you can add a 4th to filter out the drafts.
What is needed is a way to identify which transactions are drafts. The transactions table is not editable (limitation by QuickBooks) so unfortunately you can't add a checkbox to that table. Are you able to do this by using one of the existing fields? My suggestion is to use the "Wait for Sync Approval" checkbox, so that drafts aren't yet sent to QuickBooks and won't be visible on the portal. Will this work for you?
-Russell