Unsupported through the excel interface. Problem is when you create an cycle – assignment, there is a concrete data collection period. You must enter data in that range AND you must enter data at the leaf level. one workaround is collect data for the year, and stick in a month in the future. For example you want to spread 12 months of data for 2008. You create a form and assignment and collect the data and put it in Jan FY09. Then you write a business rule and you scope the 12 months with the ":" operator and the this statement points to Jan FY09. then you can divide the number equally by 12. You can get more creative with your spreading algorithm too. The only thing, is you have to submit the JanFY09 number, and then run a job that runs the rule. So its a two step process.
Howard @ MSFT selling BI 