Under Workspace Behaviour -> Screen Edges a number of edge events are available.
1. How to add another one?
2. How to make the mouse wheel scroll through available applications using Cover Switch?

What I want to do, is add 'Cover Switch' as select-able edge event (respectively an abstraction of it), and after moving the mouse over the edge, scroll through all applications with the mouse wheel.
So, instead of the Present Windows as edge effect, I'd rather activate the Cover Switch and then run through the applications with a mouse wheel, and obtain the focus (raise) the one on which I either click, or rest (for/with an adjustable delay).

Could this be configured?

1) As far as I am aware, Edge actions are determined through code, so you would need to alter the KWin code in order to add more actions.

2) Can you use keyboard keys to navigate through it? If you can, then you could probably emulate it with the mouse wheel. Best way to get this would be by filing a feature request though.