Hello,
I thought I would post a topic which outlined exactly what the "Clay Saucer" Method is;
Basically it is an alternate to using the water pan which I find provides much more control and efficiency when smoking especially in low temperatures, over night and on competitions.
I have a standard 47cm WSM which houses a 36cm Flower Pot Clay Base. Most garden centres will stock them, it may be worth asking if these fit the excel as I don't know.
http://www.comparestoreprices.co.uk/images/sa/sankey-colormatt-saucer-terracotta-10cm-4-inch.jpg
You basically foil this and place it in your waterpan. I used a lot of foil to try and create a seal.
I have to say the cost of this solution is around £5 but the savings on fuel can be recovered in two cooks!