Mass 301 redirect?

Hi,

I’m in the process of moving a site based on Joomla over to WordPress. I have all the Joomla content imported but now need to work a solution to redirect all the old Joomla links to the new WordPress ones. The Joomla links are SEO-friendly (/category/postname for the most part) so I don’t have to deal with the ? string issues.
WP is using a similar permalink structure to the Joomla site: /%category%/%postname%/

There are a couple of problems though. One is that the Joomla articles that are in a sub-category do not show the sub-category in the article links. So on the Joomla site they appear as:
mysite.com/categoryname/article-name
But on the new WP site they appear as: mysite.com/categoryname/subcategory/article-name

Another is that the sub-category pages on Joomla appear as simply:
mysite.com/subcategory/
On WP they appear as:
mysite.com/category/categoryname/subcategory/

When the site is changed over it will be on the same domain name and the Joomla content will be erased.
I have about 350 articles that will need to be redirected. I could redirect them all separately but I feel like there must be a simpler way to just change the directories being pointed at? Can this be done easily with mod_rewrite? I’m not very familiar with this process.

Any help much appreciated, thanks.