I found this help also, but, as far as I understand, it is for binding new keys for dos game and I would like to disable DosBox shortcuts - that is quite different.
It doesn't appear to be exactly what you asked for but I thought it still might be a suitable fix. Nevermind me then, I don't know how to disable DOSBox shortcuts. I suppose, since it is open source, you could edit the shortcuts prior to building it yourself. ;-p