In the Sales Tax Codes - Setup window, create a new tax code called PURSK. Its purpose is to record the taxes on an A/P Invoice, with the GST recorded as reclaimable and the PST expensed to the same account as the expense line.
Here is the setup of the tax code.
Here is the A/P Invoice in the background and the Journal Entry preview in the foreground. You can see that the $100 expense and the $5 PST goes to meals, and the $5 GST goes to the standard tax account.