--Rayrac
I think you can savvy this no problem. It's a bit like putting a bit of plastic sheathed microbore up a length of 1/2in!
As you say impossible to bypass a branch without consequences which is one of the reasons for a hiatus in the LOM programme. They need slip road or in the jargon a bifurcated device (like a Y piece) to meet the largest part of the AAA graft market. Their CE mark approved single piece device only serves a 5-10% niche. The bifurcated device approval was promised for early 2003. They also have a device for use in the thoracic area.
A picture can paint a thousand words so the two diagrams on page 12 are worth a look. Sizeable document so may take a min or two to download.