Create a Ground Rent chart of account in the Workbench -> Settings -> Chart of Accounts

It can be against a new group for Ground Rent Charges to Freeholder or one of the existing ones.
You can choose which block it should apply to or if it should be against all blocks.
Within the block, if it is not active (you can make it active when you assign it in the Workbench), ensure that it is active under Finance -> Set-up -> Block Services

Now that you have the service, you can raise a supplier invoice against yourself as the supplier or another supplier of your choice which and pay from the appropriate fund (Ground Rent