Option 1
I assume custom post type generate a URL something like this
domain.com/%custom-post-type%/%list%
So you could write it so it looks as… since the main URL doesn’t have author before custom type you would have to do this via a function since authors are dynamic
RewriteRule ^members/%author%/(.*)$ domain.com/%custom-post-type%/$1
This doesn’t specifically modify the custom post type URLs but you should be able to modify this to your need
https://gist.github.com/4336843
Option 2
or possibly if URL like this below and the custom post type doesn’t change you should be able to implement this in .htaccess and it takes the author in to account when rewriting
domain.com/members/%author%/%custom-post-type%/%list%
RewriteRule ^members/(.*)/(.*)$ domain.com/members/$1/%custom-post-type%/$2
This has a very good explanation on rewrite URL in general
http://www.addedbytes.com/articles/for-beginners/url-rewriting-for-beginners/
Option 3
Also you can rewrite the entire custom post type URL if you are not using it anywhere else… because
register_post_type();
accept 'rewrite' => array ($slug)
more info
http://shibashake.com/wordpress-theme/custom-post-type-permalinks
http://shibashake.com/wordpress-theme/custom-post-type-permalinks-part-2