Jeremy,
You'd perform the same analysis - but instead of within the Travel and Expenses Work Center, you'd perform it in the Supplier Invoicing Work Center. You might lose some detail, but whether this is an issue depends on your business requirements.
If it were a critical requirement to do extensive reporting on the actual travel and expense details, then yes, you'd have to make use of the Expense Reports with "...Paid By Company" receipt type and require that the expenses get entered through Travel and Expense, whether by the sales staff themselves, clerical workers, or some kind of external system integration.