Using the telephoto lens for shooting flowers is an excellent idea if you are kinda tired of shooting close ups or macro. We all get that feeling of running out ideas when we shoot and it often happens to me. Actually it happens to all of us. Whenever I see flowers I get that urge to get really close and start shooting macro. Though in a lot of cases, the flower as a whole is a subject that sometimes gets overlooked.
The telephoto is an excellent lens for flower shots. It's not only used for shooting animals or subjects from a distance but it is also used for portraits as it gives you a washed out background because of its long focal length. This excellent feature is why it is a good choice for photographing flowers. You basically choose a subject...shoot...and the telephoto gives you that creamy, out of focus background. The 70-200 IS USM that I use gives me the perfect bokeh, or out of focus areas all the time.
Using a shallow aperture gives you a better bokeh. I usually use an f2.8-f4 for really out of focus backgrounds. This is where a long telephoto with a wide aperture excels...that's why they cost a lot. Also some lenses give you better bokeh than others. A good bokeh is something that looks creamy...not busy.