Parameters in routing paths

Hello all.

I have what I think is a pretty common dilemma with Rails routing, and I
haven't been able to find or come up with a clean/DRY solution.

I have a home controller that is used for displaying real estate
information. I want to be able to show this information on different
platforms in different ways: desktop and mobile. I have seen similar
topics for displaying custom iphone interfaces, but that usually
involved using subdomains, which is not an option for me.

First, here is the relevant routing:

map.resource :home
map.with_options :controller => 'home' do |r| '/property/:listing_id', :action =>
    r.property_details '/property/:listing_id/details', :action =>
'details' '/search', :action =>
'search', :conditions => { :method => :post }

So what I want to do is have urls that looks like this:
/desktop/property/1 -or-

I know that I can add a route like this:
<pre> '/:platform/property/:listing_id', :action=>'show',
:target_platform => /(desktop|mobile)/i

The problem with this is that it isn't DRY, as every named route would
now need the /:platform/ prefix added to it. Additionally, every URL I
want to call would explicitly need to specify the platform, like so
(again not DRY):
property_path(:listing => 1, :platform => 'desktop')

Finally, I know you can add custom respond_to with Rails 2.0 (e.g
request.format = :iphone), but I want to allow the user to select the
format, not purely based on detection.

Anyway, if you are still reading this, thank you. I'd greatly
appreciate any sort of help. I have seen similar discussions
surrounding internationalization (e.g. /en/home/ vs /fr/home).

Thanks again.