I'm going to want to mount a sling to my M4 very soon. My question is, if I have the rear mount, (standard M4 buttstock), but not the front one; since I removed the forward post sight; would I just be able to get a picatinny-mounted front sling swivel to attach to my rail system and would it allow the strap to be connected through that and the standard M4 rear sling mount?

The reason I want to do this is because i'm getting tired of carrying my rifle from my truck to the range (just across the parking lot) in a case; and holding it would be annoying because of the occasions where I have to wait to get into the range due to a line or missing the "no shoot session" to move my rifle. I'd like to just sling it over my shoulder to make standing around with it easier instead.