Your best bet is to go the small college route. I mean, apply to a D3 or a D2 school and take a bunch of mickey classes (PE, cinema review, weight-lifting, ect...) and go out for the football team. Most small colleges have "walk-on" day where all the non-scholarship guys can try out for the team.
If you get on the team, then really try to put up stats in your games, that is really the only way you can get noticed by the scouts.
This is probably your best shot to get noticed by some scouts, it will be almost impossible to get a workout with some scouts without going the college route. I am not trying to piss on your parade here, just trying to let you know to not get your hopes up too high.
I mean, 28 yrs old with no football experience to speak of is a very, very, very tall order to overcome to make it to the NFL. And even if you do somehow make it to the NFL, at 28 most fans will want to draft your replacement (See Romo at 28 and fans wanting to use a day 1 pick on his replacement already).