Dan English wrote a great blog post about Analysis Services (SSAS) Processing and Aggregations with SSIS:
So you created an SSAS database solution and have deployed it to a production environment. Now the data has accumulated and you need to take a look at moving to a incremental processing approach because you are either loading the data more regularly or the volume of data and processing does not meet your maintenance window anymore. So what do you do?
Read the solution Dan proposes at his blog: http://denglishbi.spaces.live.com/blog/cns!CD3E77E793DF6178!2101.entry Great in depth information !