Why wouldn't he work with college admissions since he already has 4 years of experience? He also qualifies for help from the placement office. Did he not speak with anyone while at college (advisor, computer engineering department head, career services, etc.?). It seems odd to me that he spent 4 years on a major he didn't really love, and only now is picking another field (which would have to be based, one would assume, on some rudimentary knowledge of computer engineering). I realize you can't put every bit of info in your question, but I think it would be important to know when and why he decided he didn't like his major, why he didn't try to shift majors (even if it meant, say, a 5th year), what exposure he's had to computer engineering, and why he's starting all over with no idea of how to even find a program.
Some graduates get out and are just so afraid of the real world of employment and so comfortable with being a student, they just don't want to stop the life they know. But I'm assuming he wouldn't be living in a dorm as a brand new starting-over freshman, right? So this experience would be so different even if he found a school to his liking.
Where did he get the idea that a college wouldn't accept someone with a B average? Has he explored what courses he has already taken might count toward a second degree? I would think a lot of colleges would be interested in someone who has proven he can stick it out for 4 years and get a B average - but I would think they'd have concerns if he already accepted financial aid for the first 4 years and if he has not done any preliminary work on his own to search out answers. I think it's great that you, as his aunt, want to help, but if he's 22 and has a college degree and doesn't know how to at least find information, that tells me he may have some issues with determination and decision-making. No school is going to want someone pursuing a "major of the week" - they're going to want someone with plenty of gumption and not just someone wanting to take aid money that needs to go to kids who are going for their first time out.
I think your nephew should work for a while, build up a bank account, and pursue some additional coursework part time (nights/weekends). He needs to get into the real world a bit and out of the academic mindset, and get a better sense of what's out there and what kinds of decision-making skills he needs to make a better choice the next time around.
I think he might also look into a master's program. Perhaps some of his classes undergrad classes would be applicable.
I'd direct him right back to the college that knows him the best and have him work the resources and departments who have all this info. If he's not willing to do that on his own, I think you might be wasting your time trying to look stuff up on line. His circumstances are quite different from the incoming students these colleges are looking at anyway.