Pushing the level 20dB ahead of the MasterComp in order to achieve a -50dB threshold seems to be a bad idea to me, as it results in a greatly reduced bit-resolution! When mixing this can in certain cases be okay (but far from ideal!) but in a mastering situation this for me is a no-go.
i don't know which daw you use.
but you may consider, that modern daws do calculate in 32bit-float internally. that means, that you have a few 100 db of gainrange, which you can use, even in mastering. there is no reduced bit-resolution in these calculations, it is just shifting the whole audiorange up and down, which does not change anything in the audio. the recording is a digital "representation" of your analog dynamic range of let's say 96 db. inside the 32 bit float "range", it can be moved up and down a big amount, without degradation.
however, you have to watchout for a few things:
first is (should be self-explanatory) you have to bring the level down, at the output of the daw, where it goes to the "real" world of da-converters, which do have a fixed gainrange.
second, you have to watch for plugins, that do emulate real-hardware with their saturation and effects, that do occur, because of different levels. with such plugins, you will get nasty distortion, they are meant to be used with "normal" audio levels.
third you have to clear it up, if your daw is really doing all calculations on tracks, busses, master in 32 bit, which is sometimes not the case.
if this is all checked and clear, you can use the technic described without any damage to the audio, even in mastering.
to the vu-meter behaviour:
it shows the dry/wet combined amount of reduction, which is what i want to see, because that is what happens to the audio at the output of the plugin. maybe there could be an option, to switch the metering point, so it will suit your needs better.
if you do parallel-compression with an aux-bus, you will have this metering.
greetings,
mathias