Yep, it is possible to do this. I myself have done it. Back in the old days of no hench control it was alot harder. Now that you can flag your hench and pull without fear of them running past you and agro'ing several other groups it is a breeze (or at least not as hard

). Just take your time and be willing to set in a spot and watch potrols and learn their patterns.
However, PUGs are fun too. Even though I don't use them much I have joined some random groups to help them out and had a blast as well. PUGs are a strange beast indeed. I have been in PUGs that I thought would never have a chance of beating a mission and we just went through it like a warm knife through butter. And then I have been in PUGs that was set up perfect for a mission and we just got our butts handed to us.
So, for me it boils down to if I want to do a mission and make sure I get it done I will do it myself. If I am just messing around and want to help out or just re-run a mission I will join a PUG.
Either way is really up to you. Both has its Pros and Cons.
Krat