You can control DXVA programmatically using Media Foundation (MF).

In Windows 7, the MF_TOPOLOGY_DXVA_MODE attribute can be set on a topology to disable DXVA. It can also be disabled by querying the decoder for IPropertyStore and setting MFPKEY_DXVA_ENABLED to false. 

Please make sure you understand the consequences before disbling DXVA.