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1Scenario:
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3* I have a Google Account (not GMail) registered as foo@myisp.com. 
4* I want to change to GMail as my email provider, dropping foo@myisp.com.
5* I don't want to create a new Google Account, as I would have to start over on YouTube, Google Reader, Google Code, Google Docs, etc.
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8What's happened:
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10- Create a Google Account as foo@myisp.com
11- Create a GMail Account as foo@gmail.com, attached to the Google Account
12- Send an email from GMail:
13* GMail will arrive with unwanted "From:" of foo@myisp.com - no mention of foo@gmail.com
14- Add foo@gmail.com as an alternate Sender on the gmail.com account and send mail
15* GMail will arrive "From:" foo@gmail.com, but unwanted "Sender:" of foo@myisp.com
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17I can't find a way to nuke the unwanted foo@myisp.com completely. This will result in some people responding to the wrong address, which may belong to someone else in the future.
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20Some things I have tried:
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22* The non-GMail address can't be removed from the alternate sender settings
23* Removing foo@myisp.com from the Google Account and only leaving foo@gmail.com still leaves foo@myisp.com in place in GMail.
24* On deleting GMail from the account, I can't set the GMail account as the account address in advance of re-creating the GMail account.
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27I'm after a solution that works completely within GMail, and doesn't rely on my configuring any extra servers - ie, no sending GMail through a third-party smtp server.