Business Assets and NRB Trust - Not sure how to deal with the NRB element

I am dealing with an estate. The Will contains a combined BPR and NRB discretionary trust. Shares in the deceased’s business qualify for 100% BPR so will pass into the trust. The remainder of the estate is an IPDI for surviving spouse.
There is no real need for assets up the NRB to also pass into the business assets trust which will only cause complications. The problem is, there is not enough cash to satisfy the NRB, but there is a portfolio of properties. We want to avoid a situation whereby a share of a property has to be appropriated into the NRB trust to then be appointed out or loaned out.
I am wondering therefore if it is possible for the trustees to simply loan the full value of the NRB to the surviving spouse without referencing specific assets? There aren’t specific debt/charge provisions in the Will, just a general power to lend.
The alternative option is to appoint out the value of the NRB onto life interest trust but again, I am not sure if it is possible to appoint it to the existing IPDI created under the Will or if doing so will create a separate IPDI which again causes complications.
Any thoughts would be most welcome!

Rebecca Best
Progeny Private Law