In that case, you can't claim the expenses.
There is no such rule allowing you to claim the difference between this rate vs. published rate.
The rule is clear:
1. Deem the reimbursement as not reasonble (either too low or too high). Report it as income for the employee then the employee claims the full expenses on their own income tax return; or
2. Deem the reinbursement as reasaonble. Do not report it as income for the employee. Employee cannot claim the expenses on their own income tax return.