Facebook share Dialog that only post in groups

I'm trying to created an option where visitors of my website, can share items in their Facebook groups. I know this is possible via the share dialog, but the option to post it on their own wall is standard selected. I don't like that.

Is there a way, that only the option to post it in a group is available? Or standard selected? Or is there another trick to accomplish this? So visitor can easily share items in the facebook groups?

Thanks for the advices.