Solution: Laundry Detergent Bottle Caps can be transformed into a perfect shop vac attachment adapter Image 8.
Step 1: Obtain and Construct your Adapter Platform
First, I cut out the top of the lid, just enough to where the shop hose required some coercion to slip on and not fall off (image 2).
Next, I shoved the opposite end, the end that typically screws down into the detergent bottle onto the palm sander attachment.
If you notice in image 3-5 there are posts that stick off the side of the sander attachment to allow a twist and lock feature. These posts were limiting the distance I could slip the adapter on and so I used a dremel tool to fab out slots for these posts.
Once the fit was compliant I decided to leave the adapter on the sander and attach the shop vac hose like image 7. The test fit worked perfectly.
Next it was time to test it under fire with the vac in operation.
As soon as I turned on the vac it was being starved for air. With this, I backed off the distance the hose was placed into the adapter to see if this would reduce the load on the vacuum. This did not work, still to little flow.
Next I drilled 3/8 holes equidistant around the adapter. 4 hole the first time. Still to little flow. Then I put 4 more so a total of 8 and still too little flow. Lastly, I double the number of holes to 16 and the flow was perfect, no loud humming of the shop vac or overloading the motor.
See the final assembly in image blah.