re: how do I preset ddb's LINES to zero

> > try "options DB_MAX_LINE=0" in your kernel?
>
> Right.  Unfortunately that fails the "without having to rebuild the
> kernel" requirement :-)

another option would be to use say, gdb :-), to change the value of
the "db_max_line" variable from default of 24 to 0, and then boot
that modified kernel... if you find the boot to ddb is problematic.