A full size 1911 is more readily carried in a vertical shoulder holster for most folks, unless you're of Paul Bunyan proportions, in which case you may be able to use a horizontal type.
Shorter 1911s, eg. Commander size, are more capable of being carried adequately concealed in a horizontal rig, but it all depends upon your individual size and shape.
Shoulder rigs have a very definite set of CCW niches, and need be neither uncomfortable nor lacking in reasonable safety as a CCW mechanism.
For any who may be interested in such things, I've written a little monograph on the subject with comparisons of various models of shoulder rigs at
http://www.parkcitiestactical.com/shr.htm