Hi, this is not currently an API that is offered with 6.x or 7.0, I'm afraid. It's also not something that you could do in the database directly (or that would be supported).
I would suggest that you lodge a PER with Product Management. I'll email him in any case, as this is clearly a gap between functionality provided in V5 and V7.
Sorry I can't be of more help at this time.
We have a similar issue and have found that eeadmin.changeUserPassword will get the job done. The downside is that if you have self recovery on enabled it seems to reset the self recovery questions. To avoid that, we just disabled self recovery as it was very rarely used anyway. Now the users can change the password in our password management system, it pushes the command to ePO and the agent updates the password on the next checkin. This gives us a lag time of ~30 minutes between change and preboot sync.