change request user field to an email address?

is there any way to configure the request user field to allow us to enter an email address??

I have some contractors that are not given a company email, and they email in requests via their personal email. we have so many contractors come and go so it's not possible to setup an end user account for all of them.
if an end user puts in a ticket on behalf of the contractor there is no way i can change the request user field to anything else other than one of our end users in sysaid.... Thus, the problem i am trying to work around.