I've also fished the gulp sandworms/bloodworms and I usually have one rod rigged with a worm imitaition drifting along behind the yak when I'm floating over sandflats etc. It's best if there's a little bit of current/breeze to push the yak along. Works a treat on whiting and bream as the movement encourages the fish to strike. I'm sure these would work on flatties as well, but haven't caught one on these as yet.
I've found that if I'm just fishing them 'dead' in water thats not moving, the 'pickers' will get them and strip them down to the hook in no time.
Also found casting to the bank ,structure,snag or wherever you think the fish are holding up let it sink to the bottom start to retieve add
a couple of small hops and slow retieve back to the yak don't be suprised
get smashed a few feet for the yak. happy fishing fishbrain