hmc5883l to arduino uno - can't use A4 and A5- software i2c ?

Hi For my project I need to connect hmc5883l compass to arduino. Pins A4 and A5 (i2c pins on uno) can't be used because i need them to communicate to Mindstorms NXT. At first I intended to connect compass directly to NXT via i2c but it didn't worked. So I decided to connect NXT to arduino uno and from there on to connect compass to arduino. But i can't have the arduino as master(to compass) and slave(to NXT) at the same time. Is it possible to use some software i2c library to talk to compass and at the same time use Wire library to communicate to NXT?