I just ordered a padded Vickers sling, but I need a front attachment.  Does anybody know if the BFG ULoop will fit around the gas tube and barrel as a side-facing swivel?  (I'm talking with the wire going through the fixed FSB "window", around the barrel and gas tube, and back to the ULoop, not looped through itself like the girth-hitch they show on the UWL.)  Is the wire thin enough to fit between the barrel and the gas tube?  

I have a sling plate for a 1-point at the rear and I'm planning to use a MASH hook there.  Would it be better to loop the sling through the stock instead?  (I have a CAA stock and the slot is lower and shorter than on the M4 stock, so I don't think that would work.)

I could be picturing what your saying wrong so don't get mad. Basically don't place any tension on the gas tube. If your talking about running it under the tube then no I do not think it's long enough. I've seen them in person but I have only used the smaller version.

I just tried it.  My UWL did NOT fit in the little gap in the FSB between the barrel and the part that accepts the gas tube.  The wire diameter was too big.

I use the small loop choked around the front part of tbe sight. Threaded tbrough the gap, around the front & back to itself. Its a tight fit to get it installed for sure. Buf it works great.

Those slings are designed to run from the stock to FSB.  Depending on how tall and thick you are, you may have less than ideal adjustment length if you run it from end plate to front, especially the padded ones which I believe has shorter adjustment ranges because of the padded portion.

For front attachment you could maybe use a side sling adapter, or the Midwest Industries sling adapter that clamps on the standard FSB?  Ive also seen some people loop paracord onto the FSB and attach slings on there.