DTLs work in-proc rather than in-queue so you can avoid the creation of new messages altogether.

To be specific let's say you have a DTL:

<transform sourceClass='Ens.StringRequest' targetClass='Ens.StringResponse' create='new' language='objectscript' >
<assign value='source.StringValue' property='target.StringValue' action='set' />
</transform>

It would be compiled into this (simplified for clarity):

Transform(source,target,aux="") {
	Set (tSC,tSCTrans,tSCGet)=1
	Set target = ##class(Ens.StringResponse).%New()
	Do:$S($D(%Ensemble("DoTrace")):%Ensemble("DoTrace"),1:##class(Ens.Util.Trace).DoTrace()) ##class(Ens.Util.Trace).WriteTrace("xform",$classname(),"Transform","transform from source "_source_$S(source.%Extends("%Persistent"):"/"_source.%Id(),1:"")_" to target "_target_$S(target.%Extends("%Persistent"):"/"_target.%Id(),1:"")_"")
	Try { Set zVALz=source.StringValue, zVALz=$S($IsObject(zVALz):zVALz.%ConstructClone(), 1:zVALz) }
	Catch ex { If (..#IGNOREMISSINGSOURCE&&($$GetOneStatusText^%apiOBJ(ex.AsStatus())["<INVALID OREF>")) { Set tIgnore=1 } Else { Set tSC=ex.AsStatus() } }
	If 'tIgnore { Set target.StringValue=zVALz }
}

As you see the only new message is response and request/aux are not saved anywhere.

The same holds true for BPL invocations. Assuming this process:

<process language='objectscript' request='Ens.StringRequest' response='Ens.StringResponse' height='2000' width='2000' >
<sequence xend='200' yend='350' >
<transform name='dtl' class='dtl.dtl' source='request' target='response' xpos='200' ypos='250' />
</sequence>
</process>

You'll have this S method:

Method S1(process As Ens.BusinessProcess, context As Ens.BP.Context, synctimedout As %Boolean, syncresponses As %ArrayOfObjects(ELEMENTTYPE="%Library.Persistent"), request As %Library.Persistent, response As %Library.Persistent) As %Status [ Language = objectscript, PublicList = (process, context) ]
{
 Set $ZT="Trap",status=$$$OK do {
 Set iscTemp=$G(response)
 Set status=$classmethod("dtl.dtl","Transform",request,.iscTemp,"")
 If $$$ISERR(status) Quit
 Set response=iscTemp
 Do process.ClearAllPendingResponses()
 Set ..%NextState="Stop"
 } while (0)
Exit Quit ..ManageState(status)
Trap Set $ZT="",status=..ManageStatus(status,"S1") Goto Exit
}

which does nothing except for calling a Transform method. No queueing is used throughout DTL usage.

So, there are several options.

1. Do not create a new message, but rather pass your existing message. DTLs do not modify source or aux messages.

2. Use a registered, rather than a persistent class to pass values - in that case it won't be saved at all.