If I'm reading correctly, you want the top surface level, and the grooves at an angle. Is that because you want it removable? If removable, it will be remarkably easy to have it either creep down the inclined bar, or to flip off. So you might want to work out a way to hold it in place with screws. 2x6 seems pretty thick for a laptop stand.
What about using a 1x or ply going across, and attach a couple of pieces on each edge with a cutout the size of the bar. Like trusses. The front truss would be a little wider than the back to account for the bar angle. You could use a Forstner bit to drill the opening in a wider piece, then rip it through the opening to get the two pieces. Trim them to the correct height to level the top. Glue them to the top. Or, you could use a jig saw to cut the openings.
If you want it to stay in place and not slip, cut the openings slightly larger than the diameter of the bar, then line them with Velcro. Place a Velcro strip or two at the top of the bar where the truss goes so when you press it down, it stays put. All your roundovers will be identical. You can also have more room for your laptop than a 2x6 will give you and it will be a little lighter.
Last edited by DesertRatTom; 01-03-2016 at 09:18 AM.
Reason: added thought