Rifle Controller Strap Connector for HTC Vive
A strong neck clip that can be used on the Rifle Controller for HTC Vive
The modeled strap clip is easy to snap off due to the layer lines. This can be printed flat and shaped with a hot air gun to wrap around the vive-rifle-stock-attachment. You should be able to attach it to the top bolt hole.
For Fallout 4 I didn't bother printing the front half of the riffle controller, but you could likely drill or model a hole in it to allow you to attach this to the front as well.
In the images I'm using the Vive_Stock and Vive_Stock_Attachment from Modified Vive Stock