Create a new tax code called PURSK. Its purpose is to record the taxes on an AP Invoice and record the GST as reclaimable but expense the PST to the same account as the expense line. Here is the Setup of the tax code:
Here is the AP Invoice in the background and the journal entry preview in the foreground:
As you can see the $100 expense and the $5 PST goes to meals, and the $5 GST goes to the standard tax account.