As [previously mentioned](https://github.com/Shopify/active_merchant/pull/1027#discussion_r9620385), please use snake_case for custom option keys as this is what people using your gateway interface will see and is the more typical approach in ruby for this sort of thing.

i.e: 
```ruby
post[:siteID] = gateway_specific_options[:site_id]
post[:offerID] = gateway_specific_options[:offer_id]
```