Maybe it is a loose guide, but don't they get looser as the head warms up and make a rattling noise?
Doesn't blue smoke indicate combusted oil, I would have thought that oil in an exhaust would have heated and vaporised progressively as the exhaust warms up rather than combusted. Blue smoke indicates to me that the problem is going on inside the engine.
For my two-penn'oth, if it was my bike there are three things I would do, [sorry if you've already thought of this].
1/ Remove the sump plug just to see its it wet sumping, and if its not, put the plug back in and go to item 2.
2/ Remove the offending exhaust pipe [before starting the engine] to see if there is oil in there, and if not leave the pipe off and remove the plugs, turn the engine over till the exhaust valve opens and look in there with a lamp, you should see from the coke / witness marks around the bottom of the valve guide if its loose. If there are no witness marks on the Guide its probably tight, but if the valve stem is oily then its a worn guide. [you wont see what happening to the inlet valve and guide using this method but it at least shows what is going on with the exhaust valve and guide]
3/ If there is no obvious wet oil on the piston or valve or guide or coming from the exhaust port, put the plugs back in, leave the exhaust off, put some ear defenders on and start her up. You should then see if wet oil is being blown out of the exhaust immediately following start up or what's going on.
If there is no wet sumping, and the piston is oily, but the Ex valve is dry, and the Ex guide is tight, you will need to remove the rocker box to check the inlet valve guide tightness as it would indicate a possible problem here.
One question, does it make any difference whether you park it on the centre or side stands ??
Sorry that turned into a long one once I started....