Not familiar with SG series, but you can use RSTP which is compatible with PVST.
Also, maybe "Multiple STP" (see link) means PVST in the SG series world.
http://sbkb.cisco.com/CiscoSB/GetArticle.aspx?docid=6a4fdaff44f14c8f961954b903202b91_Configuring_Rapid_Spanning_Tree_on_Cisco_Managed_Switches.xml&pid=2&converted=0
HTH