Premiere Pro: Source Viewer output through Decklink?

Is there a way to play back clips in the Source Viewer which have a different resolution and/or display aspect ratio than the Blackmagic Desktop Video Setup "Default video standard" setting?

For example, my edit timeline is 1920x1080 (16x9 DAR), but I am working with source media that is not 16x9 (e.g. 2944x2160, 2.0 DAR, or 3840x2160 UHD).

When the Desktop Video Setting panel is set to 1080p23.98 for "default video standard", external timeline playback (as well as Source Viewer playback of 1080p23.98 media) through the Decklink works fine.

However, if you load in a 3840x2160 clip (same DAR, but different resolution) or a 2944x2160 2.0 DAR clip (different resolution as well as DAR), there is no playback through the Decklink via Mercury Transmit.

This is a bummer, especially now that we're editing with clients remotely, and would like to scrub through media in bins without having to drop them all into a timeline first.

I tried playing with the "unsupported frame sizes" scaling options in the "Blackmagic Device Selection" settings in the Premiere playback settings, but it doesnt seem to allow for playback of media like that.