Revision to original answer, I hadn't thought of this. No, you probably can't use beer-ready malt.
Isn't malt already germinated though? Isn't that the whole point?
The trouble with malt ready to make beer is that it's killed a fair amount of the enzyme in the drying process. Malt for beer is dried at around 70°C [pilsner apparently hotter than other types]. Diastatic malt is dried at no more than 55°C [one source said they use 40° to be safe] to not kill the enzyme.
You can make your own if you can sprout then dry 'green' barley grains before grinding.
The diastase comes from the sprouting process.
I found some DIY instructions, for if you're very keen. Making your own diastatic malt The whole process would take about a week, if it doesn't go mouldy as you're sprouting & you don't kill the enzymes by drying too hot.
I'm not sure it's something I'd like to tackle myself.
I found this - Unraveling the Malt Puzzle: Michigan Brewers Guild MBAA – District Michigan Winter Conference Joseph Hertrich January 13, 2012 which, amongst many other things, talks about trying to achieve balance between diastatic power & [everything else]. I have to admit my eyes glazed over for a lot of it; the bit relevant is towards the end.
I guess after this later discovery, the best I could say is "Try it & see".