We have just made available the ability to post to Facebook Groups.  

Because of this change, you may notice that we now request an additional permission when setting up or re-validating Facebook accounts.  This additional permission is so that we are able to retrieve the list of groups that you are a member/administrator of in order to present you your options.

Due to the great possibilities for abuse or spam, this functionality is limited to Groups where you are listed as an administrator.

To start posting to a Facebook Group, create a new route and when choosing the destination, choose a new Facebook destination. This will spawn a list of all the groups/pages/applications for which you are an admin. Simply select the appropriate one and hit save.