You have two choices:
- Change the data sources to use a SQL login and password, then you can use the built in subscription method.
- Use a scheduled app to generate the report, and have that do the e-mailing. The scheduled app would need to run under an account with permissions into SQL/SSRS.
I would only recommend #2 if you don't really need/want the users managing their own subscriptions. If the users are going to need the ability to generate their own subs then #1 is your only real option.