Hi Tina,
If for your R&D actions you would like to have a separate plant under same company code then you can create a vendor record and assign it to this plant - this is std function. Then this requisitions might be turned into interplant stock transfer orders when approved and process would be to create outbound delivery and GR it in your R&D - when posting this GR it would be consumed by WBS financially and still visible as qty stock.
BR,
Tomek