I just faced this problem on a trip to Scotland. Inspiration came from a visit to an outdoor shop (Cotswolds had just opened a store in Bournemouth)
What I did was buy two short slings, the sort of things climbers fasten their gear onto and a lenght of webbing tape, at B&Q I got two longish M8 bolts, nuts and washers.
First the bolts. At the back of the bike behind the top of the numberplate are two bolt fixing points. I put some tape, about 1 1/2 inch (the width of the slings) onto the threads, with a washer and then another washer and the bolt (to create a lipped area for the sling to sit in) before screwing them onto the bike. with the bolt screwed in up to the level of the tape the bolt can be tightened to securly fix the whole thing in place. With the two bolts in place I sliped the climbing sling over the bolt, the tape was to stop damage to the sling which easly gave two secure guy points at the back of the bike.
Next the webbing tape was measured to go under the seat just behind where you bum would be and allow for a couple of loops to be sewn in. Thread from a shoe shop was strong enough for this task. The webbing easily fits under the frame just where the tool roll is and just pokes out under the seat giving a loop either side of the seat for two guy points.
The above was much easier to do than to describe and cost no more than a few pounds and have proven so neat that I left them on the bike so I can tie down objects without needing to attach anything to the footpegs which always causes concern if about the proximity to the exhausts.
The guying points are excellent for either an elastic cargo net or for ropes, I used both for the Scotland trip and the load was secure.
Regards
Andy80F