The former England Under-21 star almost got a chance to make his Ibrox bow on Saturday when Bell injured his ankle in the warm-up to Gers' clash with East Fife.
However, he recovered in time to keep another clean sheet and continue his impressive form and Simonsen told rangers.co.uk: "Of course, it's frustrating I never got on because as a footballer you want to play in every single game that you can.
"At the same time, I know the score and Cammy is the No.1 goalkeeper at this football club.
"I'm here to back him up and he has been doing exceptionally well of late. He has kept a huge number of clean sheets.
"He hasn't had an awful lot to do in games but when he has been called upon, he has made important saves like he did on Saturday.
"Cammy has touched on it a few times himself. The most important part of his goalkeeping this season has been his concentration levels.
"He has managed to achieve what he has needed to really well and he works hard in training. He keeps himself fit and he's a great example for everyone else.
"It's one of them where I'm just concentrating on keeping myself fit and making sure I'm ready and as sharp as I can be.
"I'm sure there will be a moment when I need to go on the pitch so I'm doing my best to make sure I'm prepared for that."