If you ever get round to upgrading, you can get a separate rotisserie kit for the weber 57cm kettle.
http://www.wowbbq.co.uk/products/Weber_ ... 22274.htmlThese are quite pricey but it would give you an idea of what you can make especially if you know anyone that is any good with metal work. They may be able to make you a steel ring for your existing Q. That way you would have more capacity without the expense.
Keep the pics going, it's good to see what other folk are up to.