If speed is an issue, spread it out as absolutely thinly as possible. Every strand should have growing space, and attach it to a flat mesh. This will insure that every possible strand will have the maximum amount of nodes coming out of it. Inject tons of CO2.
Emersed culture may also help in speed. Perhaps a tupperware container thinly covered in water on a windowsill will help.
Terrestrial mosses love phosphate. Maybe added levels of this will contribute to increased growth. Maybe not. Aquatic and terrestrial husbandy draws few similarities.