I have both a big Chromega D 4x5 Dichroic, and a Saunders LPL 6600 as well. I've been trying to get a half-frame negative carrier for the 6600 for some time. I do have one for the 4x5, and so I usually use it when doing my Pen F negs. But these carriers don't come up very often.
I shoot a lot of half-frame, and I've found that a regular 35mm carrier in my 6600 is just fine if I want to use it - it holds the half-frame neg just as securely as the full frame, as long as it's in a strip. Just put the neg in the middle of the opening, and you'll be good to go.
For critical sharpness, use a glass carrier, but that can lead to a lot of spotting and so forth, unless you're a dust nazi, which I'm definitely not.
I'd recommend, also, looking for a 35mm f2.8 Rokkor lens to mount on your 6600. It was meant for half-frame, and oboyisitsharp!!! I picked mine up mint on Evibay for $80 and it was worth it. Getting that much closer to the baseboard means additional stability, and you should be able to easily do an 11x14 on the baseboard with this lens.