I have a Gmail account linked to numerous Analytics accounts, and a couple of Adwords accounts - that is, I can track stats from a dozen or so sites, and have administration rights for a couple of Adwords campaigns.

However, a client has already set-up their Adwords account and has invited me help administer their campaign. However, when I try to accept, I get the folowing error:

The Google Account xxx already has access to an AdWords account (Customer ID: ). 

As many have discovered, for some reason Google won't let an account that already owns an Adwords campaign, to join another account.

However, I wondering if there is any workaround for this? Temporarily, I'm using a separate Gmail account for this, but what is the longer term solution.

Going forwards, sometimes clients will be happy from me to 'host' their campaigns (but providing them with access), but I'm equally sure that many will want to retain greater control. Surely there must be a better way than creating an additional Gmail account for each client?

How do web/SEO agencies handle this?