This solution has been deprecated because it will not work the Salesforce Winter 16 release. Let Salesforce know you want to override the New button on the comment related list in a supported manner by upvoting this idea: https://success.salesforce.com/ideaview?id=08730000000IBFrAAO

NOTE: This solution is will no longer work in the Winter 16 release. We are evaluating workarounds, but it is unlikely that one will be available. Let Salesforce know you want to override the New button on the comment related list in a supported manner by upvoting this idea: https://success.salesforce.com/ideaview?id=08730000000IBFrAAO