Wouldn't it be easier to just keep them on the roof? Much better for installation and maintenance, not to mention concealment.
Could be. Although in this scenario, those putting it into position aren't going to want to repeatedly come back and keep checking on it. And the actual day-of, there might be a bunch of .gov alphabet soup agency snipers up there. Although, with it's NLOS and vertical launch capabilities, yes, it would be just one more pipe and/or box amongst the HVAC gear, lightning rods, and whatever else decorates the top of your average commercial building.
You're going to have to put the VIP in some sort of armored polycarbonate-laminate box, or have CWIS of some sort in the podium. Probably both.
Or, public appearances like that just become a thing of the past for anyone important, or controversial enough.
Problem with CWIS then is a head-height low angle of attack puts the innocent audience right in the line of fire of any countermeasures, kinetic or directed energy. Save for the explosives, I don't see why a group or dedicated individual with some EE and CE skills couldn't create such a system right now with COTS hobby items, and a PLC and GPS receiver.