We are working on a site in Magento 1.9. On our site we have one or two categories that should be displayed with an active filter in the layered navigation by default. Say for instance that we have a category with products that are available with or without a certain build in accessory. We have created an filterable attribute for this and customers can filter this in the layered navigation.
However, we want to be the filter to be active/applied to the categorie by default so when a customer visits the category only products without the accessory are being displayed. The customer must be able to turn of the filter so he can see all the products without the filter being applied.
Is it possible to set an active filter by default for certain catageories, that still can be turned of by vistors if they wish to? If so, how can this be achieved? We have searched for several hours on Google and found only two articles with approximately the same question but unfortunaly there weren't any solutions offered in these articles. Hopefully someone here will be able to point out how to achieve his.