By and large the private sector all over the world is left to its own devices. The nature of business is such that certain traits such as family, region, tribe etc have to be harnessed to get success. For example Pundit might prefer milk from his home area as opposed to Brookeside or KCC while a guy in Gatundu would want "local" produce. The same applies to hiring etc.
However over time even family businesses embrace diversity - even only to avoid what really killed the British Empire.
In the US the big companies had to embrace diversity to avoid negative publicity and boycotts. The same thing ended the jim crow laws where a restaurant or store served an ever decreasing number of only whites while rejecting business from blacks.
In Kenya it is the management that seems to decide which people to dominate a company. Be it a parastatal or private firm this appears to be the case. When Nyachae hired Kikuyu managers, most of his businesses ended up dominated from top to bottom by Kikuyus. Kikuyu managers of Nakumatt have hired tellers from the same tribe making it a Kikuyu company. Virtually every branch is managed by one ethnic group. I am not sure the shareholding or ownership is equally tribal.
How to end it:
For the public sector I and Pundit long proposed that an independent body made up of professionals with the requisite qualifications in Statistics, Law, Sociology, Demography etc be set up to vet all new appointments and review the existing staff constellations in relationship to the Constitution. Thus a new appointment ad can pass through that body so that the desired person is clearly spelt out. If you are looking for an Ogiek, Maasai, Njemp or similar I think it could be specified. Something on those lines
Private sector:
A voluntary body can be set up - perhaps a council with representation from a wide range of sectors. Like the public one it should have experts to evaluate the staffing policies, practices and structure / make-up and make recommendations. If the company complies it should be issued with a compliance certificate. This should be done on a continuous basis.
Companies that comply can be free to bid for state and county jobs and tenders. Participating companies may not do business with non compliant companies.
One can add such issues as may be of concern to the wider population. For example companies supporting terrorism can be determined to be no compliant. This should not be based on rumor however.