There are subsidies, which should primarily be offered to poor companies, to get them started.

The new stuff: offer the companies some "contract" or "missions". If you succeed in the given time, you get your money and everything is fine. But, even more important: if you don't succeed, you get a penalty for breaking the contract. Maybe this penalty depends on the companies' wealth.

Example: being owner of a rich company, you get a message during the game (not known to the other companies):

"New Contract Offered:

• Create an Airport in New York.
• Push LA to 15'000.
• employ 50 trains at least.
• transport 30'000 passengers

until Mai 1970. Your rewards will be:

• 10'000 cash in hand

If you break contract (that is, if you don't succeed in the given time), you will loose 50% off your liquid money." Accept Decline

Of course a company can have several missions running in parallel... if they want so ;)