Here is a site for some ideas:
http://www.naturalhandyman.com/iip/infxtra/infdam.shtm
If you had more room for insulation in the soffit areas insulation would probably be an efficient solution, however, the alternative to keeping the roof and soffit area at the outside temperature thereby preventing the thawing and refreezing that causes ice dams is some sort of edge of roof heating system. Here are several links to products which, although expensive, are effective:
http://www.deltawarm.com/rg/specs.html