I'm 6'2" and lean at 200lbs my wife is 5'6" and tiny and I could take her around town on the 690 but it would be uncomfortable for both as there isn't a lot of room. I get that comfort is an individual thing but I really don't think the 690 lends itself to regular two up riding. It's capable for sure, I personally wouldn't be overly worried about the subframe but the bike's ergos are just not very roomy. That said we've sat on the bike together but we have not ridden two up on my 690 so my opinions are best guess based on having sat on together and having applied what I know about riding around two up on our other bike. I'd say your pillion will get to look at the back of your helment when she's not banging hers helmet into yours. She'll be trying to shift forward so she doesn't feel like she is falling off the back. The seat is pretty neutral, good for you as you have bars to hold onto but your passenger will not. A cruise has a bit of a tilt to the rear, a sport bike tilts forward and both place the passenger up a little higher (normally) A neutral position for your passenger will be tiring with nothing to hold on to except you which brings back the point about banging helmets. As the passenger will be directly behind and not sitting perch up a little higher I can only imagine that her helmet will catch a lot of disturbed air at any speed over 60km/h meaning her neck is going to get sore trying to hold her head straight in the buffeting wind.
Just some things to think about. If there wasn't a couple of feet of snow down I'd try out my theory and tell you but there is no way in hell my wife is going riding in -20C weather