Bulk update Custom Object values into custom Marketo fields?

I have a Custom Object in Marketo that contains 6 fields. Using trigger campaigns, I was able to take the values from those CO fields and stamp them into custom Marketo fields. I require this workflow as the data will then sync to SFDC. 

However, the above process only works on trigger campaigns. I haven't been able to figure out how to complete a historical bulk update to transfer all values from the CO fields to my custom Marketo fields.

I know this can be done via the Bulk Update API, but I'd like to try and figure this out without the help of developers. Does anyone have an idea?