Looking back in the mailing archives
http://docs.freebsd.org/cgi/getmsg.cgi?fetch=62536+0+archive/2003/freebsd-ipfw/20030907.freebsd-ipfw
, I found a message saying that it would be trivial to add burst support in
dummynet. In that message, it says to change in ip_dummynet.c :

- if (len_scaled > q->numbytes ) + if (len_scaled > q->numbytes + q->burst_size)

I did that, even tried len_scaled = 0 But I don't see any difference after recompiling, kldunload/kldload dummynet.

I still get the same throughput with wget --progress=dot some_file