So for the actual t777s form, you don't need to provide the calculation for percent space use. Only the numbered lines are required. In which case, you could do the math yourself using the government website calculator. That calculator tells what to put in each line. You would sum the values for each line and put that into the t777s.
In TurboTax, you would have to override the fields in form view and manually put the numbers in. This might make it so you are unable to netfile.
The other solution world be to work backwards. Work out the amounts for each place and add them up. You know your average hours worked per week and can work out what % of the week is claimable. Now you can work out the % workspace you need for the numbers to work out.
Formula: claim amount / (%week worked * %workspace claimable)
If you get audited, you'll have the breakdown for each place to provide the CRA already.
