Powerpivot for sharepoint configuration: The user is not a farm administrator

PowerPivot for SharePoint 2013 Configuration gives an error 

“The user is not a farm administrator. Please address the validation failures and try again.”

MSDN says 

Either login as the account that installed SharePoint or configure the setup account as the primary administrator of the SharePoint Central Administration Site.

 Let me tell you, I have tried both and DID NOT HELP
 To keep it short and to help you faster, I will just enlist all things I have done that finally gotten rid of the error/
WARN YOU, I don't know which of these 5 actions allowed me to run PowerPivot configuration successfully. Feel free to try one at time.
Please let me know what helped you in the comments below.

 I assume that install account is the same as a farm account.
 Even though my recent hero recommends to have a distinct install account apart from farm account in real life scenarios most of the time, the account that gets installed the binaries IS the Farm account under which timer service and CA app pool is running.

So I went ahead and check account which runs SharePoint Timer service - it was, let's say, sp_farm account and then

 1. I have added (as as temporary evil) sp_farm to Local Administrators group;
 2. Add sp_farm to Farm Administrators group directly.
Before the Farm Administrators group has only built in group of local Administrators (sp_farm got belong to it, but I didn't trust the PowerPivot configuration is smart enough to get this know to)
 3. Set sp_farm as Central Adminstration site collection administrator

ATTENTION: All 3 actions  AGAINST BEST PRACTICES. After you have finished with PowerPivot configuration, please rollback the changes made for sp_farm.

 4.  CA - Configure service account -> re-select the farm account to sp_farm account and hit ok.
The page is written the way it seems that it doesn't validate that the value is the same as before, so seems like it saves the values back to config. My idea is to remind the farm who is the farm account here.
 5. Run PowerPivot for SP2013 configuration as a sp_farm account.


P.S. I have noticed that post that suggests that tool wants to have you run as an installation account. So that suggests that MSDN article doesn't reflect truth when says that you might be a CA primary administrator.