One option would be an URL parameter in the invitation to register, say ?source=employee". That reduces to one email.
Two static ists at program level to store the registrants, say, employee and prospect.
A single smart campaign
- trigger "Fills Out Form" would apply to both as well.
- flow Add to Listt
IF Email Address contains @yourcompany.com
List name employee
Default Choice prospect
The two static lists and the triggered campaign can be replaced by two smart lists consisting of filters "Filled Out Form" where the constraint Querystring is employee and teh other Querystring is prospect.