Can't put Proton switches in the Launch Options anymore

It's very common for devs and users to put Proton runtime switches in the Steam Launch Options dialog. For example:

PROTON_USE_WINED3D=1 %command%

to enable a particular game to use wined3d instead of dxvk. This no longer works with the Soldier SLR. While I wouldn't consider this a ship stopper, I think it is very high priority.