If the seat is going on top of it, why not mask off a very neat line all the way around it once it is sanded a bit in 60/80. Then use a roller and put gel top coat on, a couple of costs will colour it all. Use a smooth fluffy small roller (bandq orange ones work). The finish will not be perfect but it will have a reasonably uniform pattern a bit like a non slip. As soon as the coats are rollered on remove masking tape and although it won't look like a mirror the neat tape line will make it look intended. Even manufacturers of ribs seem to do this sometimes on transoms when they chop them down.
I've attached an example, not great quality. And not my work.