You can do this already with the attachment feature. Please check the documentation.

Use the attachment feature.

I was unable to find the documentation you referred to, if you could provide a link, I would appreciate it.

For some background, the file I wanted to attach was in "<projectname>/builds/lastSuccessfulBuild/". With the base directory being "<projectname>/workspace/", I could not figure out how to break out of the workspace directory to get into the builds directory to get the log file I wanted. For now I have simply created a simlink in the "<projectname>/workspace/" directory to the "<projectname>/builds/lastSuccessfulBuild/" directory.

Is this the intended way for this to work, or is there another method that I am unaware of?

Yes, the file needs to be under the workspace in order for the attachments feature to work. The documentation is the help button next to the item in the project configuration. It gives an explanation of how to use the feature.