Granting a lease in a will

I have been unable to find a will precedent for a gift of freehold land to A with a direction that the executors grant a lease to B before assenting the freehold.

Does anyone have any pointers?

The background to this is a desire to use the residence nil rate band where the testator has children but is cohabiting with an unmarried partner whom she does not wish to marry. The arrangement is referred to in Kessler and Ford, Drafting Trusts and Will Trusts, (13 ed.), para. 18.25.

Orlando Bridgeman
Crombie Wilkinson Solicitors