WELL, if you really wanted to do it right.. you would take the first bit of your cooled wort, do this starter method, and pitch that into the beer with the rest of the wort...Kind of a hybrid between this method and Drauflassen. *Puts down the mic, and slowly backs away into the curtain. *
When propagating from slant, using wort from the target batch is not a possibility. The bias against DME in a starter is as unfounded as the bias against non-all malt beers used to be. A 10% w/v starter contains 100 grams of extract, most of which will be attenuated by the time that the starter is pitched. The average American ale or lager is around 13P, which means that a 5-gallon batch contains 19 * 130 = 2470 grams of extract, making the extract from the starter 100 / (2470 + 100) * 100 = 3.9% of the total. Add in the fact that a starter is usually made with unhopped extra pale DME, and there is no detectable flavor contribution from the DME. The DME wort bogeyman is not going to ruin one's beer.
If one wants to make the starter media even more neutrally flavored, one can use 50% DME/50% dextrose and 1/4 tsp of a complete yeast nutrient (e.g., Wyeast Nutrient Blend of Fermax) to boost the trace element and nitrogen level. That's how I prepare starter medium (contrary to home brewing myth, one yeast is not going to forget how to produce the enzymes necessary to reduce disaccharides and trisaccharides to monosaccharides). I use MYGP for solid media. MYGP is made from malt extract, yeast extract, glucose (dextrose), and peptone (I use soytone to avoid the possibility of getting BSE tainted peptone altogether). The MYGP media that I prepare contains 0.3% w/v malt extract, 0.3% w/v yeast extract, 1% w/v dextrose, and 0.5% soytone. It is solidified with 1.5% w/v powdered agar.
Recipe for 1L of solidified MYGP
3 grams of extra pale malt extract
3 grams of yeast extract (lab grade, not Marmite)
10 grams of dextrose
5 grams of soytone (or peptone)
15 grams of agar (powder or flakes)
0.3% w/v malt extract, 0.3% w/v yeast extract, 1% w/v dextrose, and 0.5% soytone. It is solidified with 1.5% w/v powered agar.
One last thing, every minute that a wort goes unpitched is a minute for house microflora to reproduce. No brewery is sterile; therefore, people who are cooling wort to below 140F before placing it in a fermentation vessel should makes certain that their brewery hygiene is solid. While cool temperatures retard the growth of microflora, they do not stop the growth of microflora. As anyone who has left something in his/her refrigerator for a couple of week can attest, microflora does reproduce at 3C to 4C (the temperature range for the average refrigerator). Bacteria cells double every 30 minutes.