I think you have an over-simplified view of fungi and what they do. There are probably thousands of species of white-spored fungi, some "good" and some "bad" and some "neither." And any fungus that you can grow in the absence of a plant is highly likely to be a saprophytic, non-mycorrhyzal organism. They might break down whatever organic matter you have, making nutrients more available for plant uptake, but won't form a mycorrhyzal association.
Is there a link for this method you reference in your first paragraph?

--Jason

Sure,
Its actually all over gardenweb. Here is an example thread I found with a search:
http://forums2.gardenweb.com/forums/load/organic/msg0516582122484.html

Its a carbohydrate source, the same as many other simple food sources. I would think it would encourage whatever kind of fungus you would see in in your soil after the fact just in advance. Fungus feeds of plant starch sugars symbiotically anyways so would that make any compost fungus really bad?

If you work at providing a good, healthy soil the various beneficial fungi (as well as the other things) will grow in your soil without the need to manufacture them. If your soil is not good and healthy adding fungi, or bacteria, will do little since the will have little to nothing to live on and will either go dormant or die.

In the container forum, there is a thread I started that has been ongoing a few days regarding Mycorrhizal Fungi and specifically their effect on container grown plants during hot weather.

A condensed version of what we've talked about there:

Some ectomycorrhizal fungi that colonize the roots of trees can be found growing in a compost heap, but soil and leaf mold from a forrest floor are better sources of free spores for MF.

The endomycorrhizal arbuscular fungi that colonize the roots of grasses and vegatables don't grow except on the roots of plants and will not reproduce in a compost heap. Starting from a sample of soil from very healthy grass roots or a commercial inoculant is the best source to grow them from. The only way to grow them is on the roots of living plants.

For small amounts of inoculant for containers or to start growing your own, the cheapest source is Myco-Grow Soluble from Fungi Perfecti. This product is about $8 with shipping for an ounce that will inoculate up to 200 plants when dissolved in water. Many others are available, but this was the best one we could find that had lots of strains of MF and sold it in small quantities for individuals rather than commercial growers.

When mixing an inoculant with water to pour on the soil, it is probably best to use filter water, rain water, distilled water, or Chloramine neutralizer in tap water. While the chlorine and chloramine in tap water are neutralized by soil when you water plants and doesn't do much damage to soil microbes below the top inch of soil, dumping the inoculant spores directly into chlorinated tap water may kill many of the spores you've just paid for or collected.

Here are two artilces about growing your own MF inoculant
http://www.extension.org/article/18627
http://newfarm.rodaleinstitute.org/depts/NFfield_trials/0404/mf_update.shtml

Here are two articles from Texas A&M research on containers and MF during hot weather
http://aggie-horticulture.tamu.edu/faculty/davies/research/abstracts/pdfs/2005-130-jashs.pdf

http://www.hriresearch.org/docs/publications/JEH/JEH_2000/JEH_2000_18_4/JEH%2018-4-247-251.pdf

Below is the link to the thread in the Container forum

Here is a link that might be useful: Mycorrhizal fungi helps plants survive high temps in containers

10 years ahead of most!!