There might be a better, more natural workaround, but which requires a bit of tweaking/effort: using Foreskin & Erection plug-in together with Clothing Triggers plug-in, so that when a clothing item is worn, the Erection plug-in makes your AF person's genitals flaccid and small, so they can be concealed underneath the clothing, and when the clothing is detached, your AF person gets an erection. You can even trigger it using a time lapse. Not so many clothing items will work well concealing it right away (towel, bathrobe, or some shorts do), but I'm tweaking some clothing sim textures in order to achieve this properly and give a natural bulge. I'll upload it when it's ready, but it'll take time, since there's so much to test.