If you look at Twig reference about Twig extensions you can see that the render
function takes a path or a URL.
{{ render(path('route', {params})) }}
{{ render(url('route', {params})) }}
Quoting the usage from the doc "This will render the fragment for the given controller or URL".
So I would try that:
<style type="text/css">
{% stylesheets output='static/all.css' filter="?yui_css" combine=true
'@MyBundle/Resources/assets/css/reset.css'
'@MyBundle/Resources/assets/css/...'
'@MyBundle/Resources/assets/css/...'
%}
{{ render(asset_url) }}"
{% endstylesheets %}
</style>
Same approach with your Javascript files.
If it doesn't work, you'll probably want to tweak the settings of the Assetic bundle in particular the setting named use_controller
.