I don't know about with media player classic but with Zoomplayer you could. With zoom you can specify which codecs to run based on just file extension, otherwise you are trying to use two different decoders for the same mpeg2 data. (at least that's what the system will think.)
Simply define different profiles in zoom for .ts or .tp or .mpg or .ifo or .vob or whatever. Well maybe simply isn't the right word, zoom can be daunting until you get a feel for it but that functionality is there and not too hard to set up.
Is this exactly what you are asking for?
Do you find dscaler is that much better for hd? I use straight purevideo for hd and then ffdshow plus upscaling and sharpening for dvd, divx, and xvid.
In fact I haven't even tried dscaler for some time now, since ffdshow handles everything so well but I'm open to other opinions. Why dscaler and IVTC over others?