Multi platform

I have purchased the whole game including pre purchased dawntrail on pc,
But i have recently purchased a mac, in order for me to play i will need to purchase everything again just to be able to play on a different platform which is costly.
I have tried stream play but its not viable as any tecnicallity have to be troubleshooted on the source PC which is not possible as im am travelling.
Is there a less costing way apart from having to work around by installing another OS on the Mac?