I am not sure whether it is "Technically Correct", HTML4, 5 compatible or not etc. but I have always done it something like this, without any problem so far:
<?php echo $this->Form->submit('Delete it', array('name'=>'User[formaction]')); ?>
<?php echo $this->Form->submit('Undelete Selected', array('name'=>'User[formaction]')); ?>
<?php echo $this->Form->submit('Purge Selected', array('name'=>'User[formaction]')); ?>
where "User" is the model name.