Peas-in-gutters are among the many sporing chores I never get to in time!
It can be hard to push more than 12" at a time out of the gutter, but there are YouTube videos showing the attempt.
I might grease or wax the insides with something non-toxic, or include some Saran Wrap or waxed paper. I love the idea of planting 3 feet, or 5 feet at a time by "extruding" the seedlings into a trench!