Bring back the old days when it was easier and standard!
As part of the old full tilt skin you could create games of your choosing NLH, PLO, HORSE etc and assign funds out of your own account as prize money, and of course set a password, which you could pass to your friends, forum friends, or publish to the world on any website if you were so inclined.
And your created tournament would show up in the private tourney tab of all fulltilt players standard lobby.
Exactly what you are asking for right!
But those days are gone.
As people have posted above, the nearest thing available on pokerstars now is the Home Games clubs which you can create and share.
The only other way, which most
poker sites will do for you, is for you to contact their support team and politely request they create it for you.
It is probably best by email providing as much information as possible.
Why you want it. How often you want it. The value and how you propose to pay for it, etc
eg It is my birthday on xx/xx/xx would it be possible to create a private freeroll for my friends...
or for example, I run an
online poker training school and would like to have hosted on your 'best site in the world' a series of
freerolls for my members and for promotional purposes open to all your customers, kindly let me know if this is something we can achieve together etc ...
Of course pokerstars will immediately suggest you use the Home Game Feature unless you can give them some better justification as to why it would benefit them to create it in the main lobby, while smaller sites will be more helpful to the smaller requests.
You should be aware though that one of the difficulties with freerolls is they use the sites resources but aren't providing any rake.
Finally if one site says no, then you can always try another.