Ok, here's my solution.
I went to Home Depot and selected two grey 2-1/2 inch conduit couplers from the electrical department. My interior is grey, so fine. Cost: about $5.00
Th cup holders have a taper in them and I determined that if I cut a ring off the coupler just 7/8ths inch wide, it would do what I wanted. You might want to go thicker than 7/8ths, but I did not want them flush or proud. I wanted a slight recess.
The couplers have letters embossed in one end so I used the end which was blank and measured down 7/8ths of an inch and put some small tick marks with a sharpie. Then, using blue masking tape I laid a tape line along the tic marks and cut to the line with a Japanese Ryoba Saw. I selected this saw as it cuts on the back stroke and leaves a small kerf and a clean cut. The tape makes an easy to see removable guide line to cut to as you are cutting on a radius. It makes optical alignment of the saw on the pipe coupling easier and isn't permanent.
As a strong note of warning. You could choose to use a Chop Saw to make this cut, but many blades have a lot of hook angle. This coupling is very short. It is smaller than you want to hold close to a saw blade and the likelihood of the blade catching on PVC is high. Doing this could result in a very dangerous situation including the loss of fingers. Rotating blades catching and hooking is even true when cutting safe lengths of PVC. I would not advise cutting the ring off with a powered saw should you choose to make these ring adapters. I do not feel it is a safe practice.
Clean up the cut edges with a mill file. You could use sandpaper on a block too if that is what you have.
Here is Photo 1 showing the drink holders, the full coupling, the cut coupling showing the tape line I cut to, the ring I want to use and a soda can with a thermos insulator on it:
The ring is a compression fit. Here is photo 2 of the 7/8's ring installed as far in as it will go:
The inside diameter of the ring is nearly the same as the bottom of the cup holder.
And here is photo 3. Both rings installed and taking up the slack around both a regular soda can and the Thermos insulator on a soda can:
It really does take up a lot of the slack. there is just a little with the thermos insulator, a little more with the soda can. My Coffee mug will fit inside the ring as well. Water bottles like the ones from Costco, "Kirkland" brand, will fit in the thermos insulator so the will also fit inside the rings.
As I said, the rings are a compression fit and so they pull out with ease and can be stowed inside the console if larger drinks like fountain soda cups are in use.
I feel this solution will corral a lot of drinks a lot better than what is there in the first place. Like I said in my initial post, these consoles are pretty active and it is not uncommon to have your drink splash a long ways from the room they have to move in there. I consider this a huge improvement.
You may be able to find vinyl paint which matches your interior, should you choose to paint the rings you make. Auto body supply stores are a good, maybe best source for these paints if you buy local. Otherwise you can also find them online.
There were many really good suggestions in this thread and I thank you all for participating. Your ideas helped me with mine, and with your help, this is what I came up with. Of course some further slack reducer methods could be used in conjunction with this method and some great ideas were mentioned. Thanks again.
DIY: Slack in drink holder II: My Solution
~evenfall~
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