So I haven't been able to test this, but you _should_ be able to just manually build your form like so:

    {exp:safecracker channel='mychannel' return='success' include_jquery='no' datepicker='no'}
      <input type="hidden" name="mychannel-entry[row_order][]" value="row_new_0" />
      <input type="text" name="mychannel-entry[row_new_0][mychannel-field0]" />
      <input type="text" name="mychannel-entry[row_new_0][mychannel-field1]" />
      <input type="text" name="mychannel-entry[row_new_0][mychannel-field2]" />

I've assumed above that your full column name in your matrix settings is `mychannel-fieldn`. Is that correct?

NB. Taken from a [similar question in P&T's support forum][1].