Any way to force interlace output?

[Sim]

as the title, is there any way to force pms to transcode to 1080i? reason being i have some 3d sbs content which i stream to my ps3, then to a viewsonic vp3d1(like the optoma 3dxl) , but you can only select sbs on the vp3d1 when the video is 1080i , but for that i have to set the display settings on the ps3 to manual & untick 1080p, leaving only 1080i, then to play 3d blu ray content i have to change the display settings back to automatic on the ps3, otherwise no 3d blu rays.
I realise this is not hard or too time consuming but if i could get pms to output videos at 1080i that would be of great use as the ps3 would detect the change & change to the apropriate display mode wouldn't it?