creatine post-workout is ideal for the volumizing effect, but it must also be noted that in order to get the full benefit (i.e. making it worth taking the stuff at all) it should be taken throughout the day to keep the muscle saturated.
creatine is, in a sense, similar to glycogen in that it leaves the muscle tissue (usually during the same time glycogen is used). i recommend people that take it to take 5g in the morning, 10g post workout, and 5g sometime thereafter.
The problem with taking it in the shakes would be that it could stay stuck on the sides when you’re drinking the shake. (like if you take 5g and 2g is stuck on the side, some is wasted. now keep multiplying that for every time you take creatine) the receptors in the small intestine may have something to do with ‘not taking creatine w/ protein’.
it’s suggested that you should take glutamine 15m before protein for the same reason. I think it’s too inefficient this way … you’d spend your entire day waiting to take supps.
insulin spikes are dependant on your diet. e.g. people that eat 2 meals per day may only require 20g of carbs to spike insulin levels, whereas if you eat 8-10 meals per day it may require 200g for the same effect. i’m sure there are calculators somewhere on the internet, but i highly doubt if it’s an exact science. everyone’s different. I’d guess you would need.
If you’re doing it mainly to increase absorption, go ahead and take a little bit too much. as long as it’s not fructose (or, more correctly, high fructose corn syrup), it should help fill up those glycogen levels without (way) too much ill effects.