I try to do the biggest joint first - by biggest I mean the joint that will require the most heat input.
Without seeing your column I cannot be sure but I imagine that the biggest joint would be the 2" tee, this is not the information that you probably wanted to hear.
The cold wet rag works well, what I find works even better is to clamp the workpiece in a vice with the joint to be protected ( the slant plate ) touching the cold face of the vice, this will help keep the slant plate joint cold and deter it from warming up /melting.
If you do not have a vice handy, anything that is big and cold will help, G clamp, large pipe grips.
Start applying the torch onto the Tee and let the heat run across the Tee joint into the column. The theory being that you will have a short while with the joint at the correct temperature before the slant plate joint and the vice warm up.
Alternativly,
How about not soldering it and leaving it as a slip joint. I have one in the same position to allow the addition of more column hieght.
I use slip joints that I seal with a high temperature proof, alcohol resistant, elastic seal - that costs about 10p.
If you are interested, go to the local pound shop and by a silicone baking tray, the mini muffin size. ( they have 12 moulds in each tray )
Cut out the moulds and remove the bottom this will give you a band of silicone about 25mm wide that can be streched / rolled onto a 2" pipe. When it is in place it gives a good tight seal. Getting them on in the first place can be tricky, but once they are in place you can roll them up or down (think Condom) to break / remake the joint in seconds.
I have been using them for months without mishap and they seal perfectly every time.
The purists could always put a turn or two of PTFE tape over the joint before rolling on the band.

Click the picture for a bigger view
The picture is a bit vague but it is the only one I have access to at the moment. The picture is of my LM takeoff with the column to the right. The grey stripe is the silicone band. The lighter grey stripe in the middle of the band is the joint being sealed.
Toodlepip
Brian