Yes you can prepare for IAS while working by joining weekend batches or online coaching. Even i am working and i didnt have time for classroom coaching. So i joined online coaching. The coaching which i joined is Pragnya IAS institute situated in Bangalore. They provide offline as well as online coaching. .. .The institute provides live streaming of classes in virtual environament where you can also ask questions on real time basis through video conferencing. They also provide recorded lectures in case you could not attend the virtual class. They also conduct online tests and also provide updated printed material.
The faculty is very student friendly and also have commendable knowledge of the subject. They also have a library facility where even books are provided for students. The tests are similar to UPSC pattern..
Below you can find the links:
http://www.pragnyaias.com
http://www.upsccivilservices.com