Suggesting that the average ecomodder would be capable of "modifying the compression ratio" then adding a means of direct injection of fuel into the combustion chamber, which would require some serious engineering and an additional passageway in the cylinder head, is far beyond anyone outside of a considerably competent machine shop and engineering expertise, that to this point has evaded the ability of many new car manufacturers.
That being said, it may actually come to a point where the existing spark plug hole could be used if a combination direct injector and spark plug mechanism could be designed and produced.
Maybe something along this line.
transonic combustion - Google Search
regards
Mech