I have searched for this in particular and couldn't find anything so sorry if it is a repost.
This method simply requires you to use peer block to block blizzards ip. There are multiple threads telling you how to do this.
Once the i.p is blocked try to get yourself into a flex raid and you can then be kicked/leave yourself and still remain in the raid ungrouped.
However, i am not sure if you will still receive loot while not in the actual raids group, i am currently doing this now and will come back to post if i get loot.