Just use a low-tolerance yeast, like Vierka Tokay or Mead yeast if you can find it or white labs sweet mead yeast (to preempt fatbloke, yes, we know they can't claim the yeast is for mead or is of some ancient mead cultivar, it doesn't matter) and just make the O.G. pretty high so there's a good amount of residual sugar. We're talkin 1.030 with a lower-end acidity, alternatively for cheap use bread yeast, fleischmanns or red star or whatever, you'll very likely have residual sugar. Tokay yeast would be ideal as it's the kind for the Polish Mead mentioned before.
Now to thicken it more, even though that residual sugar should be pretty thick, there are a few ways of going about it. Some of the aforementioned methods are good, though I'd stay away from adding stuff like maltodextrin, you certainly can, just maybe do some reading on it and better yet try some bench trials with small measured quantities of finished product before committing to throwing it in the whole batch. Another way that's considered acceptable is to add glycerine, which you can find at your LHBS or online retailer, this will thicken it but, as mentioned before, going overboard is very possible. Again, wouldn't hurt to do bench trials before proceeding.
At the risk of sounding like a bad spam sidebar add, here's one sneaky trick you can use to improve the glycerine and mouthfeel of your wine that comes from the old school. Peel and throw in one very ripe banana, sliced or whatever, into the batch. It'll make some sludge that you'll have to carefully rack off of but one banana won't hurt, and it's a natural way to increase the amount of glycerine and overall mouthfeel without effecting flavor in a very significant way. I still recommend if you can get a hold of Vierka Tokay yeast, use properly, and make your gravity high enough, good fermentation management will produce what your friend is looking for. Just remember that high final gravity and low acidity/tannins(if you use them at any point) will make the mead really thick and sweet.
Some shameless research for help with finding Vierka yeasts
^just type in a search for "Tokay", they don't carry Vierka^
EDIT: upon further inspection Tokay is used for a sweet botrytized wine, but since it's used in sweet concentrated white wines I'm sure it'd be stellar in mead.