There's a rule that if you try to grapple something 3 or more sizes larger than you the grapple autofails. I would say if you could wildshape to make that possible, then the grapple would end.
Well, but why end the grapple now? Grapple him to death now!
Maybe there should really be modifiers for size on Escape Artist Checks.
Be aware, creatures with the Improved Grab feature get no size penalties and instead the usual attack bonus due to size on their grapple checks.
A further alternative: A generous DM could give a +10 circumstance Bonus on your Escape Artist Check for using Wild Shape to become a smaller creature (similar to the +10 Bonus to Disguise Checks).
Since you also can use all of your attacks in a grapple, you might choose a small form with many attacks to have a greater chance of yourself rolling good and the enemy rolling bad. But it will only help you in the next round (unless 3.0 hasted )