Thanks to Amit Agrawal, one of the PM's for Team Foundation, who provided this workaround for Beta3. This is useful for those that are hitting the 4MB default size limit for work item attachments. I confirmed this works nicely by trying to create a bug in VS with a 8MB attachment, verified it failed (with a nice error message), and while the bug was still open, hopped over to my AT, did this call to set it to 40MB max attachment, and then back in VS hit ctrl+s to save and it created the bug just fine.
1. Logged into your AT, navigate to http://localhost:8080/WorkItemTracking/v1.0/ConfigurationSettingsService.asmx
2. Click on GetMaxAttachmentSize to get current maximum size, if you want to.
3. Click on SetMaxAttachmentSize, specify the size in bytes and hit invoke.