Workflow trigger only works if you open and edit a record and save how can we make this trigger by mass udpate

Workflow trigger only works if you open and edit a record and save how can we make this trigger by mass udpate

We have a nubmer of new workflows we would like to update 3000 historical records, however it appears we have to open, edit, save, close each of the 3000 records for the workflow to update the fields required.  
It would be good to be able to achieve this via mass update.
How do we do this?  Because with mass update we are editing the record, so it is only common sense for the workflows set to trigger on the field update to process.