robot_localization as simple filter without fusion

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Can robot_localization be used without fusing multiple sources, ie, as a simple filter for odometry alone? I do not need or want to fuse an IMU with odometry, rather I simply want to smooth out the existing odometry.

Although the use-case may seem odd, I have a motion-capture system that gives more-or-less a real-time transform for the robot. However the mocap reported transform jitters a bit, and rarely it will jump in and out of an outlier. I could address this with a moving-average filter (too slow) or another more traditional filter (some might argue Kalman may be overkill) but I'd prefer to use the robot_localization infrastructure. In the future I may have other sensors to fuse and it makes sense to architect this system around RL.