Pretty tough to tie it up after it has fallen over & have it still look natural. You might try cutting off some of the outside leaves/stems. If you leave the cut stems 6 - 7 inches long they might provide some support to the rest of the plant & will remain hidden below the inner leaves/stems.
A.

Cutting off the outside stems is what I had to do to my Miscanthus 'Little Zebra' that draped all over the Junipers. It was my fault for planting them too close and I never expected to see the grass take off like that in the first year. Anyone interested in this plant should take the "Little" with a grain of salt. Anyway, cutting off the stems and leaving about 12" to support the remaining stems has worked pretty well for me. You really can't tell anything is missing.