It is possible to do it by writing a custom command which uses REST APIs on the WFA server.
There are REST APIs to do an on-demand data source acquisition. You can refer to https://communities.netapp.com/docs/DOC-21510 (Page 47 onwards..)
Also, note that if you have just triggered a refresh on OnCommand side, I hope you are also waiting for the monitor refresh to complete. Otherwise, the acquisition will not be useful.
Also, if you are using certified commands, there is also some amount of book-keeping WFA keeps on the type of action taken by the commands of the workflow. This is the reservation component.
So, in general, I would suggest you be careful in not calling it too many times unnecessarily as it may lead to unwanted load.