I am sure this is not a satisfactory solution, at least to me, however not considering VBA it is what I have found. Create two dummy sheets named First and Last. Place "First" in front of the first sheet that you want included in the SUM and "Last" after the last sheet that you want included. Lets say that you want to sum cell B2 from sheets 3 through 10, place First between sheets 2 and 3, place Last between sheets 10 and 11.
Your formula will always be 
=SUM(First:Last!B2)
Let me know if you have any questions.