It involves asking what proportion of the observed variance in a trait is explained by variation in genes and what proportion is explained by variations in the environment.
This idea is related to the concept of "heritability" - which is defined to be the proportion of variance in a trait which is attributable to "genetic" variation.
Of course, there's memetic variation to consider as well - and it would be nice to quantify how important it is.
If you have a definition of culture that's good enough you can use it to determine to what extent environmental factors are culturally transmitted. Then you can apply the same methodology to see what the scale of the cultural influences are.
You would then be able to say things like: in population X 80% of the variation in trait X is due to culture and 20% of the variation in trait X is due to DNA genes.
Just as you don't have to sequence every gene to get results from this methodology, you wouldn't have to identify every meme to be able to say something useful about the impact of cultural heredity. You could still make statements like: "these known memes account for 20% of the observed variation in this trait in this specified population".
Quantification would be useful. At the moment, there seems to be some dispute between anthropologists - who seem to think that culture is a very important determinant of human behavior - and evolutionary psychologists - who often seem to treat culture as simply an emergent property of DNA genes in an environment - e.g. put humans in the arctic and out will pop igloos, snow shoes and sleighs. A table illustrating the extent of the impact of culture on the variance of a variety of traits would certainly be interesting.