Actually that would be fine. If I was working in a payroll system, I would actually just base the salary of each in ratio with the current BTC price in our local currency.
Working with API or the third party ones isn't that difficult of work actually. In that way, when BTC price changes, their weekly/monthly BTC salary would vary always but still equivalent to how much they should be paid. You never want to work where you earn below minimum wage for sure.