Yap, as Gilbert said, most LL dont allow the use of subdomains (almost nobody want to list sites hosted at free hostings, and free hostings use subdomains), but for 99% (if not all) of LL's owners it is ok to use subdirectories (
http://www.yourdomain.com/lesbians/y...nsite/etc.html or
http://www.yourdomain.com/matures/yo...esite/etc.html and so on).
BTW, you could buy (with the time) a good named (for SE) domain for each niche (nowadays you can buy and register a domain name for as low as 10 dollars).
Hope it helps
Mcbethar