For any future developers.
I solved it in a different way:
1) I created a Webservice (as part of a custom DNN module, so I got the correct portalcontext).
This webservice is collecting the required information and using the TokenStoreReplacer to build the tokenized e-mails.
2) I use an external scheduleservice to make scheduled calls to the webservice.
I'ts working fine to my requirements.
I solved it in a different way:
1) I created a Webservice (as part of a custom DNN module, so I got the correct portalcontext).
This webservice is collecting the required information and using the TokenStoreReplacer to build the tokenized e-mails.
2) I use an external scheduleservice to make scheduled calls to the webservice.
I'ts working fine to my requirements.