It would really help to see the part so could give you a better idea how to do it. If you would like to use vacuum to hold the part I have found that .018 spaced at about .375 directly under the contact area will work. The bigger problem is the vacuum pump. A pump strong enough to hold your part can be as much as $2500 (Becker makes great pumps). Smaller pumps might work but I am kind of doubting it. The other way I would try is Roland makes a sticky sheet that you just press the part to it and it holds it tight. I have one and it worked pretty well if you’re not pushing the part to hard. It is used a lot for engraving type work. Stay away from a Pneumatic vacuum table as they use a ton of air. If cost is no object Datron makes a nice vacuum table. (See attached)
Hope this helps.