The pdf/excel/mail renderers are all implemented with JSF components. It would be essentially a complete rewrite to make them work without JSF. I don't think that work is currently being taken on, though I could be mistaken.
Alternatively, under Seam 3 (or under Seam 2 with my patches, search the list) it is possible to use wicket and jsf side by side in a webapp. In that case, you could use wicket for normal web pages but redirect to jsf pages when you want pdf/excel/mail rendering.