Edit~
Just so you know, one of the top champion barrel racers recently, keeps her horse barefoot. I'm sure you could find something about her, if you search barrel racing and barefoot. If you'd like a link to it, let me know and I'll look for it.
If you decide to go barefoot, allow room in your competition plans, for some time off so these cracked hooves can grow out. There's a good chance that the horse will
A. be somewhat tenderfooted just from the transition, after however-long he's been shod, and
B. the stresses of those tight turns could apply some strong pressures on the already-split hooves. I have heard of people running barrels with good times in hoof boots, but it might take some trial-and-error to get the right kind to allow serious competition.
With boots, most horses are able to transition comfortably to barefoot, and remain in light to moderate use throughout.
~~~
Shoes will most certainly not assist in growing out cracks. They will slow healing and growth, and perpetuate the stresses on the hoof that are causing the cracks to continue to form.
Try to find a qualified barefoot trimmer, or if your farrier is open to a barefoot solution, this is how to trim to grow cracks out:
First thing, trim the hoof walls short all around, then take the crack area walls out of ground contact, rasping or nipping back to the white line. Put a good breakover in, roughly at 10:00 and 2:00 or across from the tip of the frog. This will remove the torque forces that are causing the crack to continue to split up. A good short, physiologically correct hoof trim will also promote circulation, which will speed healing and hoof growth.
Do not pare the sole! It should never be pared anyway, but much moreso when the walls are compromised. The horse needs his soles to share weightbearing!
If he is sorefooted, get him some boots. If it's just the fronts, you can get by with just front boots. Movement is crucial to healing and growth! He won't move if he's sore. If the boots alone aren't enough to make him comfortable, you can add boot pads that help to relieve the pressure from the cracked walls. The pads can be cut out from cheap anti-fatigue matting. If he's sound, either with or without boots, then ride him!
Try to soak his hooves in water daily; adding apple cider vinegar 50-50 if there's any hint of thrush. If you can use those hoof boots soak. If you don't need boots, perhaps you can use buckets or shallow feed pans, or a pond or "clean" mudhole - just soil and water, no manure or urine. If you soak him in mud, rinse it off before it dries, or it will draw more moisture from the hooves. Wipe off the excess water, then apply your hoof dressing oil to seal the moisture in. Oil alone will not add moisture.
Removing the torque of over-long toes, adding moisture, and improving activity level and circulation will give your horse the best assist to heal and grow out his hooves quickly.