David, you are overcomplicating a simple procedure, its a visual pattern, doesn't matter if there is no DME, in fact when circling visually the DME may be at the wrong end of the runway! if you must have "backup" simply put a 2.5 DME arc from the landing runway in the FIX page. Aim to be 1000 at 4 miles to stabilise and be fully configured wings level by 500 latest (ideal 1000). If you can't find 4 DME the simplest way is to start the base turn abeam the arc, then with the radius of turn by the time you roll out you will be about 4 miles, judge the turn and descent to finals using the HDG track line placed over the radius of the arc. If you make the arc larger your downwind will be too wide and you may not remain visual. Selecting a "DIR ICPT" in the legs page will not show the correct DME as when you are downwind you will be outside the capability of LNAV and the path/distance is nonsense. IF YOU REALLY NEED an accurate DME then select RW EXT in the FMC and a distance/ glide angle. This is a visual pattern, but all too often guys rely on the FMC for navigation and profile..not good airmanship.