How to convert LEGO base plate to a DUPLO base plate?
The table IS already cross compatible, even though it doesn't look it. The tabletop or LEGO baseplate is cross molded for DUPLO pieces to fit and lock in on top of the regular LEGO baseplate. 

PART ONE: THE PICTURED PROOFS...

So, let's imagine the top of your table is my unopened gray baseplate.


We'll use a DUPLO Cock-A-Doodle-Doo for an example DUPLO model.


Sorry, but I don't want open my baseplate just yet, so in the next four shots we'll use these green plates to show the cross interlocking magic of LEGO and DUPLO.









PART TWO:  THE WHAT IFs...

Now, I did say the magic was cross interlocking, so... WHAT IF your tabletop HAD started off DUPLO and we wanted it to be, in our minds, 100% compatible with regular LEGO.  


You see, it is compatible, again, it may not look it at first glace, but as we can see using these White 2x4 LEGO bricks with a Bright Yellow 2x2 DUPLO brick things are indeed cross compatible.


I'm gonna get uber geeky here, but the harder to imagine negative space inside the White 2x4 LEGO brick interlocks beautify with the easier to see studs of the 2x2 Yellow DUPLO brick.      


Well, hey!  Hoped to have saved you time, money and effort in fabricating a new table.  Later!