Under the SETTINGS tab of your ranking question, untick the REQUIRE RESPONSE TO QUESTION box. This will allow you to proceed forward without any rankings.
With regards to the ranking of up to 3 items, you can set the NUMBER OF ITEMS TO RANK to 3. This will require a 1+2+3 to be inserted (duplicate rankings are not allowed). The option of ranking only 1 or 2 items is not allowed with this setting unfortunately.
My solution covers you for 0 or 3 items ranked but not the 1 or 2 items ranked scenarios. From what I can see, this is your best solution.
I have based my solution on using v7. From what I can tell, v8 does not allow this either.