Missing resolution options for fullscreen

Hello,
I understand the maximum aspect ratio for HotS is 21:9.
Now, I use Samsung G9 Odyssey monitor which has native resolution of 5140x1440 so the optimum resolution for the game would be 3440x1440. The issue is that the monitor support custom resolutions only in 120Hz mode and not in 240Hz mode. Would this be possible to allow selection of 5140x1440 (for it to render game in 21:9 3440x1440 according to the design maximum (with black bars on the sides)?
As things are at the moment I can only create custom resolution for 120Hz and then play it in Windowed Borderless mode but never in fullscreen which hurts performance and causes some G-Sync compatibility issues.
Thanks.

Just set keep scaling in Adrenalin, works for me.