Andrea Allred shows how to rebuild indexes one partition at a time:
We have had an index job that has been failing for a while. This is one of those things you really don’t want to clean up because no one is complaining, but you know you should. I had heard that I could rebuild one partition at a time, but where to start? Today, I worked my way through it, so here it is so that you can do it too.
First you need to find the biggest indexes, there is a good chance those are the ones that live on partitions. I am removing Primary Keys.
This can be a real time-saver if a majority of your partitions either are read-only or at least rarely update.