you could adjust it to point in a downward manor.
Just position it under the surface and make sure the holes are pointing in a downward position.
Well, sure ... do it that way if you prefer dead fish.
I did it that way when I installed my first spraybar. The water surface was like glass, no agitation at all. Very cool, or so I thought. I mistakenly thought my plants could generate enough oxygen for the fish, but within three days I lost an SAE and two Boesmani rainbows. (The ONLY change in the tank over the previous month was the installation of the spraybar.)
Position your spraybar horizontally, a few inches under the surface. Point the holes very slightly upward, to get some surface agitation/oxygen exchange.
It doesn't take much agitation to oxygenate the water, and it certainly doesn't result in much CO2 loss if you do it right. I have it set up this way on a 90gal with pressurized CO2 and a pH controller as well as on a 36 bow with DIY CO2. Both tanks are healthy and stable, CO2 easily stays in the 30ppm range.
(Disclaimer: In neither tank do I inject my CO2 via the main filter/spraybar output. On the 90, I use a second canister filter to drive the CO2 reactor; on the 36 I use a Red Sea 500 reactor. In both cases, the CO2-rich water enters the tank about half way down the water column.)
If your CO2 enters the tank via the spraybar and you want to point the spraybar downward to get good mixing, make sure there's some other source of surface agitation - a powerhead or something like that.