It certainly appears to work with phenidone and ascorbate in PC-TEA. At 1+50 dilution there will be almost 20 ml of TEA, which is about 17.8 grams, in a liter of working solution. There will be about 1.8 grams of ascorbic acid, which can make some kind of salt with about 1.5 grams of the TEA. With the 99% grade of TEA, the chart in the Dow Chemical manual for ethanolamines shows a pH of about 8.8 for the working solution. I have ordered some pH test strips that should help me be a little more specific as to pH in a week or so. This working solution is as active as D-23 full strength. P-aminophenol may require somewhat higher pH, but it should be in the range provided by some amount of borax. P-aminophenol and ascorbic acid are both soluble in propylene glycol or TEA. Higher pH could be obtained by using diethanolamine, but I have not tried it.
In experiments I did today, the results from HP5+ developed in PC-TEA for 8 minutes at 70 F are no more grainy than those from D-23 full strength. This is hard to show in scanned images. There, the only difference I can see is a slightly greater sharpness in fine detail in the PC-TEA, but file size limitations here would make that hard to present.