MRP order generation for items procured both internally and externally

Does anyone have a recommendation for generating MRP messages for both internal and externally procured items?  We are using Vendor Release scheduling and we have a situation where items procured from internal plants are generated on an "OI" order type vs. "OP" orders for externally procured purchases.  Vendor release scheduling appears to take the MRP generated messages and only generates the order type appearing on the detailed messages.  In some instances, we split demand both internally and externally and we are only getting one order release type generated.

Thanks!