I've seen it done a number of times like this with pipe run up the outside of the house. Personally I don't like it but if it is the only way then sometimes you have no choice. PVC tends to sag with outside use so I prefer to use emt. I don't have my reference chart in front of me but I think that 3/4 inch pvc schedule 80 can take up to 12 conductors of #12. Do you have an unfinished attic space above the second floor? You may be able to snake the wires with less damage to the drywall than you think. Is this a fairly new house with fire stops throughout? Sometimes you can drill through the top plate from the attic and through the bottom plate from the basement and get a snake all the way up. Look for an alternate route such as along a chimney chase or soil stack. Are there any closets that are one on top of the other or interior walls that do the same thing? Sometimes you can go through one of these walls or a closet and then into the attic space and snake down to where you need it.