Hi Mirko,
What you could try is to define multiple form beans in struts-config.xml with different names. i.e.
<form-bean name="AddToCartForm1" type="com.konakart.forms.AddToCartForm">
</form-bean>
<form-bean name="AddToCartForm2" type="com.konakart.forms.AddToCartForm">
</form-bean>
<form-bean name="AddToCartForm3" type="com.konakart.forms.AddToCartForm">
</form-bean>
Then in your action-mappings you use AddToCartForm1, AddToCartForm2, AddToCartForm3 etc.
Ciao,
Ryan