Limiting subform multi-select based on selection in main form

Limiting subform multi-select based on selection in main form

I am developing a database with forms for corporate data, project data, and employee data.
I have created another form to track activities data associated with a client/project by employee.

In the activities form I can select a corporation, which updates a multi-select for projects associated with that corporation.
I have a sub-form within the activities form that allows me to select an employee and record dates/times/activity for that employee, and associate them with the project selected in the main form.

I would like to limit the choice of employee in the sub-form to only those associated with the client chosen in the main form, and persist that limitation for x number of additional subform entries.

I have studied the model application "Order Management", but it does not appear to address this problem.

Can anyone help?

Peter