I agree with Tea One Sugar, with your "preferences" turn it into something that can facilitate DTD.
Have you got a bath or shower big enough for both of you?! Even if you both STAND in the bath and use the shower head - get a removable one from Wilko's or B&Q.
If he's a bit suspicious, tell him that having thought about it and btw, sorry for being so blunt last time, you kinda thought it might be a bit, um, nice to have a bath or shower together. not really for the purposes of getting clean, as it were ? maybe you could set the ball rolling.
I'm just going for a bath/shower, dear, 2 mins later - Hey, DH, can you help me and when he's in the bathroom, you can say how VERY helpful it would be if he can wash your back, and you'll do the same for him.
Result - win win, everyone's happy.