H1B Renewal visa stamping before current visa expiration.

I had my first H1B visa stamping in India and it is going to expire on September 30th 2013. However, I'm planning to get my H1B renewal visa stamping in Canada, before expiration of my current visa. So my inquiry's are, • Can I go for H1B renewal visa stamping prior to the start date. If yes, how many months/days prior to my current visa expiration ? • Would there be any risk involved, If I go for visa stamping ahead of start date? • Will I get my new visa with a date starting from my date of travel instead of Oct 1st 2013? I'm thinking of going for visa stamping in late July or early August 2013.. Please give me your suggestions regarding the above.