I have no inside knowledge but I've venture a guess that the coaches all have "contacts" with various scouting firms and recruiting services to do the necessary dirty work without them being accused of tampering. In this scenario, PJ and his coordinators probably has a few "consultants" or "recruiting services" on retainer. These consultants and their employees spend all season scouting the players, evaluating the camps, interviewing the players, etc., So at any moment Fleck can call them up and say "I'm looking for a portal QB that would fit my needs." (insert joke here about our offensive scheme) Consultant would know almost immediately who a good candidate would be and what their level of interest is and could put out more feelers. Once the player officially declares he likely already knows what his options are and what level of interest is there.
This would be for the higher graded guys or certain key positions. Just my guess.