A quick and dirty method...
I have a custom field for my products where I keep common misspellings. This custom field is searchable through my ecommerce search field.
then like every month I look through the search log records and see if there are any common misspellings that my customers are typing in. If so, then I add those to the custom field of the appropriate products.
I don't have a lot of products, so I should warn you that if you have LOTS of products this can get unwieldy pretty quickly.