Mycorrhiza generally has long been ascertain to play a key role in plant-nutirent acquisition, particularly Nitrogen acquisition. In fact more that 80% of plant species in boreal and temperate forest are associated with one or multiple form of mycorrhiza. As such i don't think inoculation of mycorrhiza will be economical.
Besides, inter-croping of nitrogen fixing plant with those that are not, is usually enough to aid the non-nitrogen fixing plant to acquire nitrogen nutrient required for there growth.