// Use additionalparams to manipulate the URL. Since additionalparams append anything to the end of the URL query, you can use 2 lines of code to trick it to do what you want.
/* Filter Lookup for Phase that has the same tractid */
crmForm.all.new_phaseid.lookupbrowse = 1; // This turn on filter
crmForm.all.new_phaseid.additionalparams = "fetchXml=<fetch mapping='logical'><entity name='new_phase'><all-attributes/><filter type='and'><condition attribute='new_tractid' operator='eq' value=' " + crmForm.all.new_tractid.DataValue[0].id+"' /></filter></entity></fetch> ";
что-то наподобие этого. Взято здесь:
http://demiliani.com/blog/archive/2006/12/29/4770.aspx