It's a long read, but I'd recommend that you look at the report that was produced for HoMFC and the council here:
http://www.edinburgh.gov.uk/download..._football_club
A couple of points from this which limit the potential for a cheap purchase and rent back to HoMFC:
Annual maintenance of the stadium in excess of £1m.
Annual dispensation given by UEFA to continue using a non-compliant stadium.
Any purchaser of the stadium would have to take into account (increasing) annual maintenance costs, already in excess of £1m, before working out what to charge HoMFC in rent. Rent would have to be at least £1.5m
You are working on the assumption that a property developer would not be able to use the land, but the report produced for HoMFC and the council states:
"Under this site specific risk assessment of the ethanol storage, the majority of the site falls out with the consultation zones arising from a major event in the ethanol storage tanks. Our assessment concludes that the effects of a major accident hazard in the ethanol storage tanks to be acceptable and should not therefore place a restriction on any re-development of the majority of the site. It is recommended that the club officials discuss the findings of this report with the local planning authority."
Basically, whilst the exclusion zone covers most of Tynecastle at present, this is based on the zone being taken from the edge of the distillery site, and not the specific risk within the distillery site (the ethanol tanks) if the zone is taken from the risk within the distillery site, then the majority of Tynecastle is out with the exclusion zone and could be redeveloped for any use. This could be used by a developer to support any development they wanted. At the time of this report, HoMFC themselves stated that the site would be worth around £8m-£10m on the open market, so I would imagine the administrator of UKIO will be looking to fully satisfy the £6.8m security they have over the ground. The FOH or whoever wishes to bid will have to come up with at least that much to get the club.