[M4IF Technotes] Lossless MPEG4?

[the_ether]

I have a special case where I would like to mix lossy and lossless video
sequences in the same video stream.
I have a stream of video, that will be encoded live. This video will include
a section with movement in the scene. This part is to be encoded using the
normal, lossy compression techniques of MPEG-4. However, at some point the
scene will be still. At this point the user wants to view the full, original
data, with no loss.
What I'd like to know is how best to encompass those requirements into an
MPEG-4 codec.
On the first frame in which there is no longer any motion the encoder would
have already sent a fair facsimile of the image to the decoder. Is there a
way within MPEG-4 to progressively build from that base to end up with the
uncompressed, original image on the client side?
The best I can come up with is when reaching the non-motion stage  to simply
subtract that image from the original, send a signal to the decoder (within
the user data?) to tell it to turn off normal MPEG-4 decoding, and then
trickle feed the difference image according to the bandwidth constraints of
the link.
It's a bit crude. Is there a more elegant, MPEG-4 way of meeting these
requirements?
Simply changing the quantiser to a value of 1 won't help as data will still
be lost by the DCT / iDCT cycle (is that right?).
Regards
Graham