subreports always display inside the main report, so they use the main report's header and footer (hence when you insert a subreport there are no page header/footer).
so how to get around this....
depending on the data, you could run the subreport and have it populate shared variables then using conditional suppress could display the values on the report in the header and footer as desired.
you could run the subreport 2x, once to get the values for the header/footer section, once to display in the rest of the page
you could create a separate subreport to gather the header/footer information to display
If you can accomplish gathering the values using running totals or some other method that doesn't involve the subreport you gather them and then display them on the last page.
From what you've written, it sounds like conditional suppression of the 'original' header / footer and display of the 'subreport' information into that area is what is needed.
Once persons opinion, hopefully a few others will offer theirs