Yes. And I know because I am one. I have no desire to marry a man because I know it wouldn't last, but sex with a guy I find attractive who digs me as me? And doesn't want to change or stalk me? O yeah. Been there. Done that. And I'll do it again ; )
Here's how to approach; Don't hit on a butch woman in front of another woman. It doesn't matter who you think she is to that woman (friend, lover, whatever) don't do it. All of our relationships/friendships are every bit as important to us as yours are to you, so show some respect.
Wait until she's alone to talk or start up that chatty relationship at the gym or wherever. Tell her you think she's hot/sexy and you'd do anything she wanted and it would stay between the 2 of you. Be willing to get the hotel room or whatever if that's what it takes. Just the offer to be that chivalrous goes a long way as it shows you are serious and "adult" about your offer and it's nice if you're the one always doing everything for someone else to step up. In fact it's hot.
Let her think about it. Don't push with ultimatums or whining. It's disgusting. Most masculine women idolize the male mystique/masculinity more than straight women do. If you act like a little "b" it will likely be a turnoff. Let her know the offer still stands and you are for real but be mature/macho about it.
Some women sit back, consider the offer and watch a guy for awhile. See how he is with his buddies. If she sees you running your mouth to your friends/coworkers about who you get with and what it was like, etc etc she may very well turn you down as she doesn't want all that going around about her. I turned down a very handsome, body like a greek god guy who was obsessed with me for that very reason. He talked too much. A lot of guys lose hookups due to that. hint. hint. dudes....
But let the ones you like know you are respectful of their lives, willing to rock their world and available...and most of all DISCRETE. good luck