Magento - How to add Layered Navigation to Advanced Search?

There is no quick solution for this. The standard search and the advanced search use two different methods to search.

If you compare the layouts in catalogsearch.xml you see that for catalogsearch_advanced_result the block catalogsearch/layer is not included. If you copy the block definition from catalogsearch_result_index and change the root template to 3columns.phtml various errors are thrown.