Manfred,
I don't have Mosets Tree available for testing right now, but I've used it a bit in the past. To add the buttons to the Detail and Summary views you'll likely want to modify the MTree template files. A custom field may be possible if you add a simple label or other non-editable field and simply add the {JFBCLike} tag to the output. Never tried that honestly. It's a good idea and would love to hear if it works.
If you can't get that then modifying the template shouldn't be overly difficult. It may take a bit of effort though. The files you'll want to edit are:
/components/com_mtree/templates/<YOUR_MTREE_TEMPLATE>/sub_listingDetails.tpl.php
and
/components/com_mtree/templates/<YOUR_MTREE_TEMPLATE>/sub_listingSummary.tpl.php
Once in there, you'll need to find where you want the social buttons to display. Once there, simply add them like {JFBCLike}{SCGooglePlusOne}{JLinkedShare}{SCTwitterShare}. They should just appear on the front-end. If they don't look right, just let us know the page to look at and we can help you style them (put them in a row, make them bigger/smaller, etc).
Hope that helps get you started!
Alex