Can I create a compressor preset for maximum bitrate below a specified file size?

I need to create some videos that all, regardless of their length or resolution need to be below 50 MB each. Currently the only way I've found how to do this, is to set the Avg. Bit rate setting to Custom, and then to manually play with the slider until the Estimate file size at the top is below 50 MB.

Is there some way to specify a maximum file size and have Compressor automatically determine the bit rate based on the video length?

[Re-Titled by Moderator]