It may be possible in MT...you could be out there a few days before deer opener hunting antelope and scouting for deer, or wait til later in the season/deer rut and hunt both...

Eastern WY I think it would be possible on private land by paying a trespass fee, but I'm not sure about a DIY public land in WY without any bonus points...WY has walk in areas, ie private land open to the public, which may be an option for eastern WY...where a lot of the tags are leftover due to the private land...

Without bonus points, I'm not sure how nice of trophies you'll be looking for / chasing.