Step 1: Just Do It
The first thing you need to do is to find something to raise one end of the table so that you get a small incline along its longest dimension. You can experiment with the amount of incline that suits you best.
Then you make sausages from the PlayDoh and make the buckets that the marbles should land in. Make one long sausage into a semi circle and put that at the top of the table, so that you can shoot marbles at it and the marble will follow that round path. Now you are basically done. You can ornament by putting the scores beneath the buckets. You can also put small amounts of PlayDoh as pegs and other obstacles basically anywhere on the table.
Make sure to involve your kid in every part of the process since his or hers ideas will make for exiting additions.
Now play and refine the design, and when it is time for dinner you can clean the table in a minute!