To think the whole thing further, in addition to the explanations::
If you do so like described from @log1c and assign the defined command to a service, the service inherits the whole fields from the check command. So you can write the website directly to the service.
Or, if you write this information to the host object, you can access this with the macro $host.vars.[field name]$.
Which brings us back to the point that we have discussed here: Apply Serivce multiple times depending on a dict/array? - #3 by Killerloop 