Kiri:Moto also slices for belt printers. I don’t know whether @stewart has addressed that particular problem (making the primer line a few layers thicker? I dunno) but he’s certainly built another slicer that supports belt printers.
Yep, KM has a lot of belt-specific features. Two that are really important are leading anchors and side brims. You can also change most settings on a per-layer or per-layer-range basis. So you can over-extrude the leading-edge, for example. The leading edge anchor can be turned into a wedge shape so that it gets knocked off by the scraper instead of pulled around the roller causing later print failures. This is a feature unique to KM.