Platform is *supposed* to have BuddyPress support, so I looked at the CSS route via Firebug. Sure enough, some minor tweaks “lifted up” your sidebar to where it’s supposed to be.
Add this to your stylesheet to lift up the sidebar.:
#buddypress-page #content {
float: left;
width: 600px;
}
If you want to bring in the BP elements that extend the horizontal border, etc, add following to stylesheet as well to start:
#buddypress-page #content .padder div.pagination { margin: -20px 0px 0 !important; }
#buddypress-page .item-list li { padding: 1em 0 !important; }
div.item-list-tabs { margin: 25px 0 20px !important; }
div#subnav.item-list-tabs { margin: -15px 0 15px !important; }
ul#members-list, ul#groups-list { list-style-type: none; margin-left: 0; }
Add other styles to taste.
If the above solution works for you, please close the WP.org forum post as resolved. Cheers.