multiple stores/ssl mismatch

first - thanks to those that helped me get my base store running - works like a charm.

i've been reading through all the posts on multiple stores with one checkout (ie different themes, audiences, url's, etc) and there doesn't seem to be a good solution quite yet (although absolute seems to be very close). i need to solve this asap, so i've decided to install another instance of zen-cart in another folder of the main site.

so - we have http://mainstore.com and http://mainstore.com/ministore where ministore is a SEPERATE install of zen-cart (yes, i know - it's a pain, but the only solution i can see right now - please let me know if there is a solution i'm missing). configuration.php is set to use http://mainstore.com as the webserver and https://mainstore.com is the secure server. HOWEVER, when accessing http://www.mainstore.com/ministore, i get an invalid certificate warning - i assume because the certificate is issued to mainstore.com and not mainstore.com/ministore?

do i have something named incorrectly in configure.php? should i just scrap this plan and do something else?