During a live draft, it is not possible for the commissioner to make selections for other managers. When logged into the draft applet, the commissioner will have the option of drafting for his/her team only.

The commissioner does have the option of making "keeper-style" pre-draft player selections, however. Before the live draft begins, the commissioner can go to the Commissioner's Tools page and select Edit Pre-Draft Selections. He or she will then be able to assign specific players to specific teams.

So, if your keeper league allows teams to keep three players, the commissioner can enter the first three rounds before the draft begins. The remaining roster spots will be filled during the draft like normal.