The majority of ladies on AW will see you for just a BJ service. I'm like yourself, a fan of oral. Just message and ask if they'd be okay with that as you're interested in oral only. 99% of them said yes to me. Keep in mind not all girls can continuously do that for half an hour though, usually they'd be open to a 15 minute booking of the sorts (so would be good to target the ladies who offer 15 minute bookings).