Just add the following snippet to the Render section of the RSReportServer.config file and you'll have a new option to render your subscriptions.
<Extension Name="CSVSemicolon" Type="Microsoft.ReportingServices.Rendering.CsvRenderer.CsvReport,Microsoft.ReportingServices.CsvRendering">
<OverrideNames>
<Name Language="en-US">CSV (semicolon delimited)</Name>
</OverrideNames>
<Configuration>
<DeviceInfo>
<FieldDelimiter>;</FieldDelimiter>
</DeviceInfo>
</Configuration>
</Extension>