if I understand your question correctly, you want to run an on-demand workflow against a list of contacts in a spreadsheet.

Then there are a few options here:
1. use SSIS + Kingswaysoft, use excel data source and use KingswaySoft destination to execute workflow based on the contact id.
2. Use a temporary entity in Dynamics where you have a lookup to contact (to resolve based on the contact id) and then run the on demand workflow against them. once finished, delete the records.