First: Do you have any other baseplates? Those small one's are not very good and tend to show the work table or something off set if the cameraman isn't careful. If you have any other bigger baseplates, I suggest using them.

Second: If you don't have any bigger ones, but you have some other smaller ones like the ones you talked about above, I suggest placing them side by side. Depending on what you're filming, you'll want one to mirror the other. If you place them side by side theis will create a bigger baseplate.

Third: If all else fails, use that baseplate! You just need to space out the furniture/oddsnends evenly. Go look at Nathan Wells's Bricks In Motion Tutorial videos and also take a look at his Alex and Derrick films. The latter was filmed on the baseplate you speak of and the vids might be some help.

-EH

what does it look like? do you have an image?

To make it look bigger than it is, I'd make the camera angles closer to the subject in the shot. Also, I'd make the objects in the scene either far back on the baseplate or close to the subject, as putting it all only right in the middle will make it seem like you're short on space.