I'm guessing you need to smile at the wiki admins and get them to install the MediaWiki Maps extension
http://mapping.referata.com/wiki/Maps
Alternatively contact the developers of the installed SlippyMap extension and see if they'll address this line of code:
if
<code>if ($marker) $error = 'marker support is disactivated on the OSM wiki pending discussions about wiki syntax';
syntax';</code>
as I can't find any discussions on the wiki (why not just mlat and mlon as optional?). MediaWiki suggests future development of this plugin is unlikely, but not sure where they got that information from.