Any way to get "one-shot" callback events? (Instrument callbacks)

I'm trying to figure out how to manage the multiple callback events from a serial-port object.

I have a serial-port object with a BytesAvailableFcn that's triggered when there are a sufficient number of bytes in the input buffer. The incoming data-rate is moderately fast (a few 10s of kb/s), but incoming packets could be as small as 12-bytes. If I set my BytesAvailableFcnCount to be as small as 12-bytes, I get drowned in the overhead of processing the callbacks (i.e., one call for every 12-bytes). If I set the BytesAvailableFcnCount larger (say 100 bytes), then the problem goes away (but I lose the ability to respond promptly to short packets).

What I'd really like to do is just limit the callback events to be a one-shot event that I would manually re-enable when I leave the callback. Is there any way to do something like this?

I've tried a workaround that has helped a little bit:

function my_data_callback(port,event)
%Prevent multiple invocations of callback
if port.UserData.is_processing
    return;
else
    port.UserData.is_processing = 1;
end

%do some stuff

%Exit and re-enable callback
port.UserData.is_processing = 0;

But even touching the port object like this has too much overhead (profiling this reports a lot of time spent in serial.subsref and other object validity checks. I can do similar sorts of things with persistent variables, but debugging then becomes difficult.

Any thoughts?