[SalesForce] URL hack – create & save record without viewing edit screen

Since you are already using a VF page for helping the approval submission why not create an method with return type of pagereference in your AgreementApprovalRedirect extension and use it to redirect to the desired page?

The code would look something like this:

Approval.ProcessSubmitRequest req1 = new Approval.ProcessSubmitRequest();  
req1.setComments('Submitted for Approval');
req1.setObjectId(agreementApprovalId);
Approval.ProcessResult result = Approval.process(req1); 

if(result.isSuccess)
{
  return new pagereference('pageURL');
}

It's a bit of a hack, but you could create a Visualforce page and controller action that will redirect the user to the most recently created Task for a record.

Set the &retURL going into the task creation to send the user to this new VF page and include the parent opporutnity record ID in the query string.

/00T/e?what_id={!Opportunity.Id}&retURL=%2Fapex%2FredirectLastTask?rId= {!Opportunity.Id}

public with sharing class redirectTaskController {
    string recordId = '';

    public redirectTaskController() {
        recordId = ApexPages.currentPage().getParameters().get('rId');
    }

    public PageReference redirectToTask() {
        PageReference activityPage = new PageReference('/' + recordId);

        Task[] recentTasks = [SELECT Id, CreatedDate 
                              FROM Task WHERE WhatId = :recordId 
                              ORDER BY CreatedDate DESC LIMIT 1];

        // Check that the new Task if fairly recent.
        if (recentTasks.Size() == 1 && 
                recentTasks[0].CreatedDate.addHours(1) > Datetime.now()) {
            activityPage = new PageReference('/' + recentTasks[0].Id);
        }

        activityPage.setRedirect(true);
        return activityPage;
    }
}

Visualforce Page

<apex:page controller="redirectTaskController" action="{!redirectToTask}" >
    <p>Redirecting to task</p>
</apex:page>

Another idea would be to create a Visualforce page that uses the Task standardController and provides a custom save action.