Copy either username or password to clipboard on per-entry basis

Many sites prompt for username first, then password. So currently, after browsing to the URL for an entry, we have the password in the clipboard, rather than the username, so we need to go back to pwsafe and copy the username via several clicks, then re-copy the password later when the site prompts for that. It would be nice to have a per-entry flag / option to copy the username rather than password when one hits the Browse button. Thanks.