Something like that is possible.
Case 1 : using Marketo "create SFDC task" flow step:
From Marketo, you will not be able to do much. From SFDC, you might, but the data model might be tricky, because there are some limitations on what you can do on the task/ activity object and on the campaign member one. You also have some limitation with the task fields that can be populated from Marketo (no custom fields, and not even all the standard ones...).
You would have to log the campaign ID in the task description or subject, then have an APEX trigger that parses that value and reassociates.
Another possibility would be to create an SFDC web service that does the job and call it with a webhook.
Case 2: using Marketo automated task creation set in the admin > Salesforce section
In this case, you do not have the slightest possibility to influence the task content, so forget about it. Using this feature is not recommended anyway, as it clutters your SFDC without adding any real value and creates so many tasks that the real ones (created by humans for human follow-up) becomes hardly usable.
Thank you for the background! Hopefully at some point they will update the task fields to mirror what we have in salesforce. Right now it's pretty basic.