Remove entity from post before binding it - symfony

Question

Let's say I have a main form (foo entity form) where I have an embedded form (bar entity embedded form).
Let's also say that foo - 1/many - bar (of course).
Now, I want to display all possible bar entities in the system, even if they aren't associated with foo. So before bind form with foo entity, I usually do some query, extract data and, if bar isn't already associated with foo, associate it (basically i create some "virtual" association that haven't to be persisted under certain circumstance. I can't use symfony2 native method as I need to handle some attributes and Symfony2 don't let me do that)
All works like a charm. Now I added to bar form a non-mapped field that should help me to know whenever to save or not the association.
Into controller I check for the presence of this field and if not, I artificially unset the index of the collection from request object. When I dump the request all is good (embedded elements without flag aren't there anymore).
BUT
When I bind request object to entity, all embedded form elements are still there. This is driving me totally cray.
Code example
(I will not paste entity code as the issue is not there. I will not paste form code also)
public function createAction()
{
$foo = new Foo();
$foo_form = $this->createForm(new FooType(), $foo);
if ($request->getMethod() == 'POST') {
$parameter_array = $request->request->all();
$bar_array = $parameter_array['foo']['bar'];
//If I dump here, of course, all bar are setted
foreach ($bar_array as $index => $bar) {
if (!isset($bar['associate'])) { //this is the flag
unset($parameter_array['foo']['bar'][$index]);
}
}
$request->request->replace($parameter_array);
//If i dump $request->request->all(); all non-flagged bar are gone
$foo_form->bind($request);
$foo->getBars(); //If I dump this all bar(s) are still there (even the not-flagged ones)
}
}

Answer 1

I've found a workaround. As I can't controller - or at least it seems I cannot - directly parameter bag when entities are involved, I've simply act upon object after form and object are binded.
My code is now this
public function createAction()
{
$foo = new Foo();
$foo_form = $this->createForm(new FooType(), $foo);
if ($request->getMethod() == 'POST') {
$foo_form->bind($request);
if ($foo_form->isValid()) {
$parameter_array = $request->request->all();
if (isset($parameter_array['foo']['bar'])) {
$bars = $foo->getBars();
$bar_array = $parameter_array['foo']['bar'];
foreach ($bar_array as $index => $bar) { //Of course here
if (!isset($bar['associate'])) { // I can use array_filter
$bars->remove($index); // or something similar. Is just more readable that way for this answer
}
}
$foo->setBars($bars);
}
}
}
}
Is there a better solution?