I'm not 100% sure but I think the MCE receiver will only accept codes that it's original remote sends. If I understand your question correctly you already exhausted those codes. If my assumption is correct you cannot get more IR codes from that remote. However, maybe you can make some of the IR codes dependent on the state of your system. For example play can work for DVD and for CD player without needing 2 different buttons.
Does this make sense?
A solution would be to purchase a USB-UIRT, which will receive IRcodes from 99% of the remotes out there.
No support through PM