The custom button can be created with the global variable $Site.Prefix. This will return the path of the current community.
/* Super Clone */ {!URLFOR($Site.Prefix + '/apex/dh_superclone__superclone?rid=' + MyObject__c.Id + '&cfg=MyConfig')} /* Super Clone Pro */ {!URLFOR($Site.Prefix + '/apex/lcrm-scp__scpclone?rid=' + MyObject__c.Id + '&cfg=MyConfig')}