Add SQL Custom variable in alert to address

Hi all

I want to use a custom propertie value in the alert email action To address field.

That has been discussed before and you can just add a variable there to get the address.

BUT I want to add some logic there and therefor add a custom SQL variable.

I got one that is working perfectly in the message body but Orion say it's not valid in the address field.

${SQL: select ISNULL(Contact_Person,''Support@company.se'') from NodesCustomProperties where nodeid=${N=SwisEntity;M=NodeID} }

Above would send alert to a node-specific person in custom propertie IF there is one, otherwise to default support address.

Why can't I do that? Limitation in GUI or engine?

(Tried to edit in sql table directly under orion.dbo.Actions.Description but that didn't populate up to GUI, why?)