Perhaps landlords may be willing to sell window space such
that other businesses can market themselves. Maybe a long
shot but it would be better than boarded windows and as the
high rents seem to be partly causing the problem you'd be
talking to them in a language they understand.

I've tried today to speak to an owner who said that their 
shop was 'being renovated' (!) and that what he does in 
the future was 'his business'(!*£) I think that 
Shropshire Council should get tough on 
these 'landbankers'. The one I spoke to lives in 
Nantwich, so it's 'out of sight, out of mind'