I have multple accounts on agent OS, and often need to use the same email address. For example I have my own contractor account, as well as a multiple landlord accounts. A very common solution is to use the + in emails - anything after the + is discarded by the mail client, but is allowable in RFC822.
I would use simon.topple+contractor@mydomain.com for example, which is a perfectly valid email address.
Could you look at changing your validation rules to allow this. + signs are perfectly valid within RFC822 (providing the mail host accepts them) and their exclusion via web page validation shouldn't really happen.
(as a side effect, I don't want emails addressed to me as a contractor to be attached to my landlord account!).