**** UPDATE ****

I have now added a third line, about 4 feet long, to the bridle ring and removed the "dogbone" described below. I now have the two lines coming from each bow cleat and a third line (forming a "Y") with a loose bitter end.

Instead of pressing the anchor line through the ring and inserting the block, I use the new line as follows:
After setting the anchor line on the center cleat, I bring the bitter end of the third line through the bow roller bail to a convenient spot on the anchor line. There, even with the anchor line under tension, I can easily tie a rolling hitch with the bitter end (4 ft) of the newly added line. I then let out the anchor line until the two bow lines take the strain. The center cleat is left connected, but slack. I have used this arrangement now 4 times, two of which were in 20 knots of wind. None of these times did the center cleated anchor line ever become taught, indicating the rolling hitch was working perfectly.

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I spent a lot of time thinking of ideas that would allow me to have an anchor bridle that had its normal advantages of keeping the boat pointed into the wind and distributing loads, etc. But I was interested in a bridle arrangement that would preserve the center cleat attachment as a back up. What I came up with was partially taken from some discussions I had over on the multihulls listserv.

I took two 35 foot nylon lines and spliced a 12 inch eye into one end of each. At the other end of each I spliced a thimble AFTER clipping the thimble onto the largest stainless steel ring I could find. The result was a SS ring with two 35 foot lines connected to it, each line having an eyesplice in the other end. Also attached to the ring via a lanyard, is a piece of teak block with very smooth notches cut out of it - kind of like a dogbone.

The idea is that the main anchor rode remains attached to the center cleat as normal. This is also the starting position for attaching the bridle. Next, you put the two eyesplices over the cleats on each hull. The center ring is brought through the bow roller as shown in this picture.

 

Now comes the hard part..... Pull up enough slack on the anchor rode to allow you to put it through the ring, inserting the "dogbone" underneath. You then let out more of the main rode and allow the assembled ring to go out over the roller. The resulting maylay looks like this. Note that the "dogbone" has enough room for the thimbles on the inboard side.

And here is the bridle fully deployed. The center rode can stay slack while the bridle keeps the boat centered. If there is any problem with the bridle, the center rode is still attached to the center cleat as normal. Now (as expected) ..... I only tried it out one time (shown here) and the main anchor rode might be slipping through the ring some (the center rode kept slowly losing its slack). I'm not sure what I will do if this is the case - maybe trade the "dogbone" for a third thimbled line and use a rolling hitch to the main rode. I also might try wrapping the main rode around the dogbone twice instead of just the one hump.