I'll take a slightly different tack on this, as 1) some others have said they enjoy it with an element of embarrassment and 2) I'm a longtime straight male switch but love my switch Domme ex to treat me as a sub and give me large, long submissive enemas mixed with our other kinks. This often meant her dressing me in head to toe latex suit, hood and gloves plus another kink of ours, thick rubber sneakers like Converse Chucks over the suit. Then I'd be cuffed to keep me immobile and after a lot of finger and plug ass play, she'd put in an enema DBC and inflate it to make me hold one large or two smaller enemas (both held together, no release in between). Then there's a long period of verbal taunting and physical chores to let her enjoy watching me struggling through them holding the enema. The idea was to make me feel as submissive, helpless, embarrassed and humiliated as possible which we both enjoyed very much.
Usually no mention is made of feminization except sometimes she'd refer to me as her "little subbie enema girl" or the like to accentuate the submission. I or she never felt degraded by this but actually enjoyed it as part of her temporary but intense consensual Domme-inance over me that day. We would switch on other days so I could let her enjoy being the same kind of enema sub on other days.
Now I'm not a cross dresser nor was I asked to, but if my female partner the next time wanted to really try to make me feel feminized as part of our D/s kink/enema play, I'd love it. She could just start our whole session with her intent to feminize me temporarily with our other kinks. If we planned ahead, she could dress me in either a female rubber wetsuit or latex suit with breasts and/or also put me in a female cheerleaders uniform with a skirt, then change the sneakers she made me wear either with a women's style or color of sneakers. The whole time of course she'd be referring to me as a girl and making me as feminine as possible. Knowing her and some other ideas I've read here, she'd also frequently taunt and embarrass me by her intent to make me look as pregnant as she could with as large an enema as she wanted in me.
"You remember how I usually fill your belly and show you your distention and then make you hold it while I make you do chores and give me orgasms?"
"Of course, ma'am, you always make it hard to do and humiliating."
"Well this time, little girly sub, before we start that, you're going to have to look very, very pregnant for me. I know for sure you can hold 4 quarts and even did 5 for me once, so I'll be sure to measure it this time so we know how to make you look pregnant whenever I want............"
"Yes, Mistress, whatever you need to make be feminine for you today." Of course as is our usual, I'd be moaning groaning and begging not to be a girl and not to have to look pregnant to no avail. If she really was enjoying doing this to me, she'd probably reply with something like
"Oh, yes, my little subbie rubberized enema girl. You'd better get used to me turning you feminine this way pretty often from now on. After I fill you with your beautiful huge pregnant enema and start making you give me orgasms, I want to be fucked by a sexy female enema slave today. That would be you! And we have all night to make you feminine, so I can do whatever I want to make you a girl. And don't even think about an orgasm for yourself until you look as feminine and pregnant as I like.""
"Yes, Mistress, I know I always need to make you happy and well-fucked before me. Thank you, ma'am."
I'm solo for now but a) it's a very powerful fantasy for giving myself enemas, and b) if I'm lucky, my next Domme partner will enjoy it as well.