OK, I've found that the easiest way is to simply duplicate the styles at
/connections/resources/web/_style?include=com.ibm.lconn.core.styles.oneui3/base/standaloneVcard.css
and the enclosed sprite images, then use loadCssFiles=false
instead.
This adds the classes:
lotusui lotusui30dojo lotusui30_body lotusui30_fonts lotusui30 lotusSpritesOn
to
<span id="semtagmenu" role="tooltip" style="...">...</span>
which in turn targets the hover triggered Business Card only for styles.