This script parses out the first Lead Source from a comma or semi-colon separated list and then gets the Lead Source ID from an xRef list.
Function ScriptedField
 Dim ls
 Dim res
 ls = "@@ORG:CUSTOM07@@"
 If Len(ls) <> 2 Then
  If InStr(ls,",") > 0 Then
   ls = Left(ls,InStr(ls,",")-1)
  End If
  If InStr(ls,";") > 0 Then
   ls = Left(ls,InStr(ls,";")-1)
  End If
  res = ls
 Else
  res = XrefRead("sf-LeadSource",ls)
 End If
 ScriptedField=res
End Function