Perhaps you haven't read the rules. Below is a direct quote, bold added for emphasis.
C. Equipment and Positional Shooting
1. Unless mentioned in the course of fire, any equipment may be used. The only exception to this is tripods and shooting sticks, which are never allowed. NRL22 shooters are considered to be the most welcoming participants in any shooting sport. Sharing of equipment, especially to new shooters, is highly encouraged. The bipod is not considered equipment and is part of the rifle system; however, it cannot be used to support the rifle while shooting in any unsupported position. The bipod does not have to be removed while shooting in an unsupported position. A sling is designed to provide a way to carry the rifle and also to assist in unsupported positional shooting. The sling may attach at 1 or 2 points to the rifle. It may have cuffs or adjustments to aid in unsupported positional shooting. A sling is the only authorized piece of equipment that may be used in any unsupported position.
ETA: In fairness, I wouldn't be mad if a MD looked at a walking cane bolted onto my buttstock and said "...no way." As with almost everything, MD discretion tends to govern.