If you are only limited to the parts that came in the box, you could put some anti-wear grease inside the stock plastic dampers. This can take away some of the bouncy nature of the dampers depending on how much grease is used. This is what I've done when I've raced with those type of dampers in Eurotruck racing. The TCS rules allow using grease or lube on any moving part in the Eurotruck class.

As was already stated, there are ways to affect handling with traction compounds or the use of super glue on the sidewall/tread of the tires.