Why are you sleeping in bed with girls if you're not trying to fuck them.
Doesn't make sense. If she's in bed with you, she's already accepted the fact that you guys are AT LEAST VERY MINIMUM making out while cuddling. There is literally no better situation to escalate physically with her then cuddling. She knows it too.
Unless your friend zoned x1000 you should be escalating.
If I'm cuddling a girl, or in the same bed as her. We're making out and I'm escalating to have sex with her. If she refuses to make out, then I don't cuddle her it's that simple. I don't show her any affection. Then try again. 2 strikes and she's out though.
Now if she gets LMR, there's tips to get around that on the forums.
Girls don't put themselves In positions like that sober, unless they're okay with the possibility of sex or at least hooking up.
Now to answer your question..
If you get a boner, who cares. Girls like boners, girls like knowing they turn you on, it makes them feel sexy. Don't be scared to rub it on them, or have it rest against there butt or whatever because they like it trust me. Make sure she knows she is turning you on they love it.
Especially spooning, rub that shit all on her ass, & whisper in her ear that she turns you on. (Only after already making out or other sexual escalation!) Then tell her to turn around, when she does, take her hand and put it on your package. She'll either comply or she she won't, but either way, you're winning.
Now I want to make it a specific point that you DO NOT touch her with your boner before you even kiss, or touch her, or even start cuddling. That's just weird and she'll be like really? We haven't even kissed? That would be no different then like the previous poster said, just whipping it out on her.