After brainstorming for a long time and taking a bunch of measurements I have a plan. I decided to just extend the table by 12". More would be nice in certain circumstances, but it would need to be about 24" in order to use the couch as mealtime seating and anything between 12 and 24 would make it such that you couldn't use our normal "stool in the isle" mealtime seating.
I had a section of 12" wide shelf board that's 3/4" thick to match the existing table and cut a length that matched the width of the existing table. I rounded the corners and edges to match the shape of the table and will be giving it a nice finish.
For supports I ordered these: Metal Drop Leaf Supports, Pair - Cabinet And Furniture Door Catches - Amazon.com
The plan is to mount them under the sides of the existing table so they can pull out and be the main support for the extension. But when not in use they can be pushed under the existing table and hopefully not be in the way or bang knees.
To lock the extension in place I ordered these: 2 Pcs Black Metal 3" Long Door Lock Sliding Barrel Bolt Black - - Amazon.com
The idea is to drill a hole in the inside of the supports and then mount these on the underside of the extension so that when in place I can slide the bars into the holes in the supports and the bar will hold the extension in place on the supports.
How sturdy this ends up depends greatly on the quality of these supports and I may have to do some tweaking once I get them in the mail. I'll take pictures after getting it rigged up and report back on how well it seemed to work. The hope is for a stable extension to the table that when removed won't get in the way of it's existing function.