Cullen was suspended one game by the team and an additional game by NFL commissioner Roger Goodell, who also fined him $20,000 as a result of two preseason arrests in 2006 -- one for the drive-through incident, one for DUI.
Goodell deemed it "conduct detrimental to the league."
The two cases resulted in fines and 10 days of community service as well as a judge's order to attend outpatient treatment and Alcoholics Anonymous meetings.
The Jaguars consulted with Goodell before setting things in motion with Cullen, who was an assistant coach at Idaho State last season.
In a letter to Jaguars owner Wayne Weaver, Goodell said:
"Joe paid a heavy price, and rightly so. But to his credit, throughout this process he has always accepted responsibility and has willingly embraced the result as an opportunity to become a better person and role model. Not only has he fully complied with the obligations that were imposed on him, but he has undertaken several others on his own ..."
"Having had the benefit of several conversations with him as well as reports from a number of sources, I think he is an example of our primary objective under the policy-to provide assistance and support that ultimately rebuild reputations and extend careers. I have little doubt that he will continue to progress and will represent the Jaguars in a positive manner."
It's unclear where Cullen would fit on Del Rio's staff as the Jaguars already have Ted Monachino, who's been overseeing the defensive line since 2006.
Paul Kuharsky covers the AFC South for ESPN.com.