I would imagine that all he is interested in is the longitudinal CG since he's probably trying to decide where to place the wheels on the trailer. The vertical CG wouldn't matter much since there is little room for adjustment there.
If the lift has scales in each of the lifting webs, what you need to do is record the weights and carefully measure the positions of the lifting webs from a fixed reference point on the boat (say the tip of the bow). Then it's easy:
*multiply the distance from the reference point of each web by its recorded weight.
*add the results of the two products together.
*divide the result from above by the total weight. This result is the distance of the CG from your reference point you chose earlier.
Piece of cake.