KG, can you plant out and cover with horticultural fleece?
And yes, I agree about the overbearing monster Pampas. Mine has been too big for a few years now, (I also have a monster Laural, Ceanothus and Cherry tree that need hacking back this year).
Obviously, we planted these things in complete ignorance and at the time, a small plant in a huge garden didn't seem to be a problem. I had absolutely no knowledge of pruning for many years or even owned a pair of secateurs so things were left to grow. The Pampas also provided privacy and I have such a big garden to fill that it took up space in a very cheap way.
It's incredibly hard work removing the rotted stump, but it doesn't suit my style anymore, which is quite formal with a splash of romantic, and if I'm honest, I will only miss the plumes. the rest was ugly. Hubby is already budgeting for the trellis and arbor and I'm busy trying to get my vision onto paper. It will be the first time I have ever actually planned a border, usually I buy plants I like and then wonder round for weeks or seasons trying to figure out where it should live. 
So I will take all the time I need to get the structure planting right because they will grow and be a trouble to remove...like the Pampas.