I am installing a clay paver walkway from my front porch to the driveway. I am using the standard dry method with a compacted stone base and screeding overtop. The topography is such that making the walkway flush with the driveway would create too steep a slope, so I plan on having the walkway end about one paver's depth higher than the asphalt. Essentially, there will be a small step up to the walkway when entering it from the driveway. My question is, how do I keep the "step" from moving. I can't install the plastic edging, so I thought I might have to use mortar on the last course, kind of like a retaining wall. Any hints on how to do this?

You can use a soldier course, which os individual bricks put in standing sideways on their ends which acts like a footing. Most people will tell you it's safer to use a minimum of two steps because it's easier to see and people won't trip so much, or add a hand railing and paint that first row a contrasting color

I would form that step with concrete if you want it to hold up, masonry block might work too. You should try to keep the step 7" or less or have 2 if there is more than that.

The small step will be a stumbling block, especially for strangers. Can the porch end of the walk be lower, to reduce the slope? Is the walk long enough that you could put a reverse curve into it and eat up some of the drop?
An 8% slope is acceptable for wheelchairs. I know I am redesigning here but I would do anyhting possible to avoid a small or even normal sized step.