If your mount has a polar scope then aligning that on SigmaOctans will be fine for piggyback. Failing that the drigt alignement technique that you already seem to know how to do is the way to go.
Here's a very detailed site on drift alignement. You can skip all the technical rubbish and go striaight to the instructions!
http://members.aol.com/ccdastro/drift-align.htm
Cheers