Risolto!
Forzo il download e poi cancello subito. Tutto nello stesso file .asp

<%@ Language=VBScript %>
<%
NomeFile=Request.Querystring("file")

function getBinaryFile(fileSpec)
Dim adTypeBinary
adTypeBinary = 1
Dim oStream
set oStream = server.createobject("ADODB.Stream")
oStream.Open
oStream.Type = adTypeBinary
oStream.LoadFromFile fileSpec
getBinaryFile= oStream.read
set oStream=nothing
end function

response.contenttype="application/x-unknown"
response.addheader "Content-Disposition","attachment; filename=" & chr(34) & NomeFile & chr(34)
response.binarywrite getBinaryFile(Server.MapPath("/public/tmp/" & NomeFile))
%>



<%
'CANCELLA IL FILE
Dim fso
set fso=Server.CreateObject("Scripting.FileSystemObjec t")
Dim file
file=Server.MapPath("/public/tmp/" & NomeFile)
if (fso.fileExists(file)) then
fso.DeleteFile(file)
end if
%>