You/they'll need to check the paperwork... the entry fee [ASO] covers your repatriation costs separately to your medical costs... so getting back from Peru to Colorado shouldn't be a problem - however, the hospital fees while he is still there might be, as ASO only cover the first €4500.00 of medical bills, the rest is up to you/your own insurance.
Therefore, I'd suggest he gets out of hospital in Peru as soon as he can, and gets back to the USA, where his US insurance can take over any additional medical treatment.
A similar thing happened to me in 2011 - I was in hospital for 8 days in Chile before they would let me fly home, and those costs (together with the surgery etc) is what ramped up the bill... while ASO covered the repatriation costs themselves.
As a thought, does Kevin not have [a degree of] insurance through is FIM licencing body? My additional insurance costs were ultimately covered by the British ACU who issued my 'permission to start' certificate, and which fortunately includes insurance for both liability and medical costs in just such cases.
Hope that helps,