If you replace the accessory detail button with your custom button, then you can call the accessoryButtonTappedForRowWithIndexPath: method.
example - put this in cellForRowAtIndexPath (when setting up cell):
UIButton *myAccessoryButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 125, 24)];
[myAccessoryButton setImage:[UIImage imageNamed:@"yourImage.png"] forState:UIControlStateNormal];
[cell setAccessoryView:myAccessoryButton];
[myAccessoryButton release];
cell.accessoryType = UITableViewCellAccessoryDetailDisclosureButton;
and then as a separate method:
- (void)tableView:(UITableView *)tableView accessoryButtonTappedForRowWithIndexPath: (NSIndexPath *)indexPath
{
//do something
}