I think that is the same procedure as for a arduino on 8Mhz. change the settings in the arduino settings file to the corresponding speed ie: change
build.f_cpu=16000000L
to
build.f_cpu=1000000L
and reprogram the fuses to make use of the internal clock of 1Mhz.
and of course be aware that the timing in the arduino code is totally wrong. everything will be 16x slower.