i just took care of this myself over the weekend. she is going through her 3 month growth spurt, so i decided that she's waking up anyway, so might as well get her off the swaddle. i prepared myself for a few sleepless nights.
now that my baby is starting to grab things, her startle reflex is not as severe as it was about 3 weeks ago when i tried to get her off the swaddle. so over the last couple of weeks, i left one arm out for a week, then wrapped her arms at her chest so she would be able to get both of them out herself. she's been wriggling out of the swaddle forever, so i knew she was capable of sleeping without it.
but when i finally put her in the sleepsac, i would watch her on the monitor, and when she was falling asleep and i saw her arms flailing, i would go in and gently hold her arms down while she fell into a deeper sleep.
it took a couple of nights, but it's totally worked. she's been off the swaddle for 4 nights now, and only wakes up once to feed at about 2.
good luck. it's not as bad as i thought it would be. but it definitely helps to wait until they have some kind of control over their arms when they are awake.