I've been soldering for 37 years, nearly on a daily basis, and I forget not everyone has this level of experience. I also was certified under the NASA 2000 standard, and spent many months in school and qualification testing. So, I've also been "school trained" for high-relability soldering.
Above are some quick examples on what I did, looks like.
I use Kapton (Polymide 33) tape. Kapton (polymide) tape can typically withstand 7500 Volts, is made for continous use at 356 Degrees F (there are some higher temp rated Kapton tapes, fyi).
Some examples:
http://multimedia.mmm.com/mws/mediawebserver.dyn?6666660Zjcf6lVs6EVs666exXCOrrrrQ-
http://rocky.digikey.com/WebLib/3M/Web Data/5413 Tape.pdf
Where does one obtain it?
http://www.mouser.com/search/refine.aspx?Ntt=polymide
Search on digikey for Polyimide or Kapton
5419 has an advantage over 5313, as it has materials in it that greatly reduce voltages generated when removing the tape, which can exceed 10,000V typical of many tapes.
I simply polish up the surface with steel wool or 3M scratch pad, until it is shiny and clean, and rinse with hot water and soap to remove particles. The copper will take on a light pinkish color when it is properly cleaned. Keep scrubbing for a while beyond where the copper looks clean.
Then I put kapton (polymide) tape down to electrically isolate the ends under the CREE. I then rub it down (burnish), until things look crystal clear, showing that the adhesive is properly attached to the copper.
It takes a good amount of heat to heat up the plate, and I use RMA flux solder (DO NOT USE ACID CORE), and melt it on the area, assuring it is hot enough to flow to the copper and sticks. You want the solder to flow as you apply it, not just melt it on top. I use two soldering irons or a soldering iron and a paint stripper heatgun from Harbor Freight that goes for 9.95. Take your time and don't rush things. Right before I apply the CREE, I like to use the iron as a slag bar, and wipe it across the top, to remove the oxides (slag).
Removing the other heat sources, I keep one iron on the plate to help hold temperature. I then take tweezers and set the CREE on the molten solder. Sometimes I put flux on the back of the CREE, but it really isn't needed, and thus I don't use it much. You can also pre-tin the back, but this takes skill, as most irons are much hotter than what the CREE should be exposed to, and the lack of thermal mass makes this a dicey operation. This tape prevents the solder from flowing across the copper, and works better if you rub or burnish down the tape.
Once the solder flows to the CREE, I then brush on isopropyl alcohol to quickly cool the plate down. Sometimes I use forceps/pliers/tongs, to pick up the plate and set it on shallow water or isopropyl alcohol. Not deep enough to wet the LED though.
I suggest you solder your wires to the CREE ahead of time if possible, or at least pre-tin the pads (I usually connect to the top side).
As I mentioned in the other thread, if I was learning, I'd highly recommend that you get a hold of several of the low cost red CREE LEDs, XL7090 or XR7090 for practicing the technique.
If you are going to be soldering on your CREE LEDs, make sure that you have "dehumidified" (baked) them first, or they were stored with desiccant and the indicator still indicates things are dry. Failure to do so, will result in weird things to the gel and phosphor inside, and a dramatic loss in light output. It can also result in color shift in the output. This is not a problem if you are not soldering them.
The process for dehumidifying them is found here, bottom of page 3:
http://www.cree.com/products/pdf/XLampSolderingandHandling.pdf