Yes! There is a special priority you can assign your programs (ForegroundServer Mode) via DosSetPriority() which will give your process (note, not thread, but process) the maximum allowable CPU time.
Another route is to use DosEnterCritSec()/DosExitCritSec(). Calling the former will disable thread switching (hopefully for a short period of time), and calling the latter will enable thread switching again.