Cell-o-fill, yes you can use as a sub,  it will result in a slight difference in colour.  Cab-o-sil and cell-o-fill are stronger than wood flour though if you were to have a failure it would be the wood, not the fillet.  I actually used cab-o-sill for my deck to hull joint and most of my other fillets.  I also put the tape on when the fillet was still wet so there no sanding issues.  Cab-o-sil is a rock when it comes to sanding.

As for drill fill drill, the entire purpose here is to keep the wood and water seperate.  You are basically looking at do I use epoxy or silicon to create that barrier?  It is an extra step and takes a little longer, but consider all the hours of careful sweat only to have a water stain.  I'm a big fan of the drill fill drill method.  There is an additional risk, silicone and varnish do not get along so when it comes time to re-varnish your boat, no silicone is better.  I've talked to a couple of experienced boat builders who reckon silicone has no place on wooden boats, use a good non-silicone caulking if you want to go the belt and suspenders route (I did)

I have a bunch of leftover wood flour from a 17LT. Send me your address and I'll send you a container, email is  jonathanATswampsdieselDOTcom

Swamp

Thanks for the offer. I am planning do it this weekend. Someone wants me to finish the doors to an entertainment center that was put on hold for the WD. What is she thinking!? :) 

Brian