Hi Jesse! Just a couple of notes about "Cambridge Blue Lobelia" itself. It is not a trailing type, but rather grows in a clump about 12 - 15 inches around. It is an annual, but is known to reseed. It also is very dangerous if ingested.
If you plant this plant on your hill with the burlap, cut a hole in the burlap for each plant so that it can get it's nutrients from the soil. They like a ph level of 6.5 - 8. They also need to be watered consistently. Otherwise they will do fine.
If you are looking for a wild spreader that is going to cover your burlap in no time at all and stay that way, "Cambridge Blue Lobelia", although very pretty, is not the plant you need.
Hope this helps! Feel free to get back with other questions anytime!