Hi Alex, I'm not aware of a way you can set up Data Sources with specified Windows Credentials, however, you can run BIDS using "runas /netonly" to impersonate a user for network operations. It would look like the below:

c:\>runas /netonly /user:domain\SSRS_QA "C:\Program Files (x86)\Micro...\IDE\devenv.exe"

This will run all network operations through BIDS impersonating the specified user, including data-sources, while keeping local operations and settings as you.

One caveat is that if you use TFS (as I do) or similar it will use the impersonated credentials to connect to the TFS server and fail.