can I use a coupler to a parchament cone??

I would think so, just as long as you can push that first thread past the bag. I don't see why it wouldn't work.

yeah, i've used them with parchment bags

yep, our instuctor taught us how to do it easily...take your cone and drop your coupler in it, then cut a hole just big enough for the tip to come out. Then screw on the other piece of the coupler - remove and it will have crimped the paper showing you where to trim it and then you are good to go.