You should treat the second “gig” as a separate contract and the employee as a contractor for the project to avoid issues with employment standards.
We would recommend compensating this position based on a project rate or piece rate as well.
Considerations
1. Think about the possible impact this could have on their salaried role performance; what are you going to do if they are tired from working all night on the secondary gig and underperforming in their salaried work?
2. Be clear about expectations and that there is no cross-over between the 2 roles. The employee cannot double dip and do gig work on salaried time.
3. Be clear on how performance is evaluated in each role.
4. Have the employee submit an invoice for the gig work.