Other than migrating to Fusion Lifecycle Modern,
This could be possible with some of the Forge API's (Viewer, Model Derivative [MD], or Data Management [DM]), but it would take some development...
With FLC Classic you could embed an iFrame into a field.
The iFrame would reference an external Forge Viewer that shows your Attachment.
Ultimately, to use the Forge Viewer, you need to send the file to the Model Derivative API to translate it into the format the VIewer needs (SVF) and then store that SVF somewhere your viewer can reference it (Fusion Team, FLC Attachment, etc...), so "Not having to store it someplace else" might not be possible unless you migrate to FLC Modern.
FYI: With FLC Modern connected to Fusion Team, when you upload a file to Fusion Team, this all happens in the background.
There are several examples on Autodesk's Forge development site that show how to build a website to host the Forge Viewer, and interact with the MD & DM API's.
Autodesk Forge: https://developer.autodesk.com/
Autodesk Forge GitHub: https://github.com/Autodesk-Forge
FLC Modern Disclaimer:
Although Modern FLC is in production, as of today (3/17/2017) it does not have all of the features that FLC Classic has. The good news is, most of these features should be available later this year.
Fusion
