I agree with lshick and david. The key to sealing the bolt holes will be a good seal with the bedding compound of choice. I would recommend butyl for this as it has the most elongation of any bedding and with the leverage of stanchions this is an issue. A small leak every 5 - 10 years isn't that big a deal as long as the balsa doesn't get wet. It sounds like you've beat that problem with epoxy filling in its place. When you drill the bolt holes countersink the top of the holes a bit. What this does is create a "o-ring" around the top of the bolt hole.
As far as street poles - they do it the way they do so the pole can be easily replaced in later years without access to the bolts - not really applicable to stanchions. Here's a link to Maine Sail's excellent tutoria; on the best way to do this.
Re-Bedding Hardware Photo Gallery by Compass Marine at pbase.com
Brian