StreamDevice and AMSG field

["Neidherr, Dennis Dr. via Tech-talk" <tech-talk at aps.anl.gov>]

Dear all,

and again a small question:
According to the documentation there is a (new?) field called AMSG to store alarm (or error) messages. Is this somehow also useable with StreamDevice? Because this field is marked as "non-writable", I can not simply redirect errors into it like I tried here: 

setAmplitude0 {
    out ":SOUR1:VOLT %f;:SYST:ERR?";
	in "+%(myAgilent:ErrorCode)i,\"No error\"";
	# @mismatch { in "%(myAgilent:ErrorCode)i,\"%(myAgilent:ErrorMsg)#s\"" }
	@mismatch { in "%(myAgilent:ErrorCode)i,\"%(AMSG)#s\"" }
	@writetimeout { disconnect; }
	@readtimeout { disconnect; }
	@replyTimeout { disconnect; }
}

I can certainly use another record to store errors but with the AMSG-field this would be a more elegant way. So, is there some workaround or have I maybe missed something? 

Thanks and
Greetings Dennis