I think this would need a safety review. Just about any of the standard (for small bore / full bore) sling attachments are designed for easy release at the sling-swivel handstop. If the sling has to remain attached then I would regard that as a serious trip hazard or hazardous from the point of view that while donning the sling could lead to the rifle being dropped, etc.
It isn't obvious to me just how a sling should be used in FT since "steadying" might mean only using the sling angled down from the attach so there is no vertical weight support i.e. you would be pushing against the sling with an upward (or horizontal) force when kneeling (how would the marshall rule on that?).
I would love to use a sling and shoot prone but so many lanes are just cleared (grass/twigs) for sitting and up :-) Meanwhile I can't imagine shooting .22RF 50m/100yds competitions without a sling even if the wrist pain is common and a real concentration breaker.