You can estimate, though it'll be tough to be 100% accurate. That's okay. :) There's likely not enoughu calories in these things to worry overmuch.
Figure out the calorie content of the mixture first. You can enter it in Sparkrecipes.com into the recipe calculator. You should already know the calorie count of cucumbers.
Add the cucumbers. Let them do their thing. Next, remove the cucumbers, and measure the remaining mixture.
The difference should be the amount the cucumbers have soaked up. Voila! There's your calorie count for the actual cucumbers.