Custom wordpress admin (built from scratch)

I have used wordpress for a site that eventually grew up to a multi-purpose web app (along with the presentation theme), so a custom admin was necessary for the enduser (the one who pays a monthly subscription).

Given the fact that I am only using wp-load.php as my starting point (built on bootstrap custom theme), and utilizing the functions of wordpress (wpdb, custom post field updates, nonces, etc) how can I bring up a plugin page, or install one of your plugins but have access to my admin?

My admin is installed in a second folder admin2g on the same level as wp-admin (actually it is there but I have used redirections to do proper login/logout for specific user roles, the administrator still uses wp-admin).