As others say, get the businesses to do the pitch.
In the meantime, some ideas:
Local ‘branches’?
If the nearest Evans to your main office is miles away, point out the benefit of local shops and ‘try before you buy’.
Range
Range is a good sales point too. The Evans range will be relatively limited. Opening to a wider network of LBSs gives many more options and brands.
Competition
Is your employer in competition with any of Mike Ashley’s businesses? It’s unlikely Evans were part of the Ashley empire when they signed up to the scheme. Could now be a conflict?
Etc etc
On the negative side, some of the schemes (Cycle2work?) require participating LBSs to accept C2W vouchers but take a 10-15% cut, so whilst some may think they are supporting the LBSs, the reality is that they are just piling on low margin sales for lots of admin and grief.