During the De-gassing phase excess carbon dioxide is given off..... until the beans more or less stabilise.
Sure reduced pressure (applying a vacuum) will cause this gas to be given off faster.... but a very important element (which gives espresso the taste and aroma) are the volatile oils in the beans...... and these evaporate slowly even at room temperature and atmospheric pressure. Reduce the pressure and these will boil off a lot faster.... and leave the coffee flat tasting.
De-gassing is a natural process..... and just like many other natural processes..... is best left to occur at its own rate. Speeding it up is not a good idea (why is it we want everything to happen "yesterday"!!!)...... just roast a little earlier and let nature take its course would be my advice.