I think we should bring in a guy who is familiar with the our Minnesota Vikings. A guy the Vikings Front Office brought in years ago, to develop him into a potential QBotF. That's right, Shaun Hill! You thought I was going to say Tarvaris Jackson, didn't you...
Shaun Hill was originally picked up by MN as an UDFA in 2002 and stayed through 2005. Hill was our 3rd stringer behind Daunte Culpepper and his slew of backups to include: Brad Johnson, Todd Bouman and Gus Frerotte. Scott Linehan was the Vikings OC from 2002-2004, and during that time Hill got to learn a pretty explosive and vertical offense.
Then in 2006 he was picked up to be the 3rd string QB for the 49ers, according to his wiki page. Hill stayed in San Fran from 2006-2009 and saw a lot of turmoil because the 49ers changed offensive coordinators/scheme every year. But going back to 2006, it was none other than Norv Turner as his OC. 2007 they ran the WCO. 2008 the 49ers hired Mike Martz, another well known coach from the Don Coryell tree. In 2009 they brought in some guy named Jimmy Raye. He apparently ran some version of the spread which appeared to benefit Vernon Davis, and only him.
From 2010 through 2013 Hill was backing up Matt Stafford under Scott Linehan again. His offense has also been kinda hard to nail down but from what I've read it's a version of the "One Back Spread" which fundamentally is very similar to a Coryell offense via formations and personnel. And since Calvin Johnson is in that offense he's incorporated a few deep routes to use Johnson's skill of attacking the ball in the air. But since it uses similar personnel and formations it would mean Hill would know pass protection schemes he could pass on to our rookie.
With all of Hill's experience with Coryell based offenses I think he would be the best QB for the Vikings to bring in and mentor a young guy. He brings a lot of system knowledge he could pass on. He should be able to pick up Norv's playbook almost immediately, and show our rookie how to execute in Training Camp and if need be start over the kid until they're ready. I think a 2 or 3 year deal similar to Cassel's would be best, and having a veteran who isn't learning the offense right now would be a GIANT leg up in this offensive install.