Solr query parser that allows specifying multiple default fields

Question

I would like to use the Dismax query parser because it allows me to specify multiple default search fields (using the 'qf' parameter) as well as other nice features such as field boosting.

However, I want a query parser/scoring algorithm that takes the sum of all field scores, rather than just the max.

Is there a way to configure DisMax to take a sum of scores rather than the max?

Can I specify multiple default search fields using the standard query parser?

Is there a different query parser alltogether that would achieve this?

Do I need to write my own query parser?

Any help is greatly appreciated.

Thanks!