Hello @Mark van Dijk ,
As stated by @Vicky Kumar (Mindtree Consulting PVT LTD) , currently wildcard search feature is not supported in graph API.
However, you can raise a feature request for the same using below link :
https://feedbackportal.microsoft.com/feedback/forum/ebe2edae-97d1-ec11-a7b5-0022481f3c80
Hope this helps.