no, its already twisty enough, drilling holes will make it worse, the Cardinal profile is notorious ( at leaast in my experience) for being twisty ish in the tail

How about drilling (hole saw) lots of big holes and sheeting with 1/64 ply? 

Dave,
The problem with lighting holes is they don't save that much weight if the wood is normal 4-6 lbs stock and you give up stiffness. It also can mess up the CG and require adding tail weight. If you do some holes then sheet the sides (before shaping) with 1/64" ply you will just about break even on the weight and gain a lot of stiff. If you go this route, use slow cure (say 2 hr) epoxy, applied to the plywood, use a playing card to scrap off the excess epoxy (you only need to just see the surface damp not covered in epoxy). Use an ACE bandage to wrap the fuse/ply or heavy weights along its length. When you install the stab use 3/8" fillets top and bottom to add stiffness to the stab (I would add 1/2 oz glass cloth over the stab or carbon vail). Good luck.

Best,   DennisT

Mine is an ARC kit from 2005/6 and has big cutouts in the rear part of the fuselage. The stab and elevators are built up as well. Result being a very light model, 45 oz ready to fly with a 9.5oz battery on board.

The thing flies like its on rails, there is some twistiness but it's not evident in flight.