Theoretically you could use a common hook spanner (or C-spanner) in size Ø 96 mm or an adjustable one with matching range.
Unfortunately, perhaps you noticed already, do the “noses” of usual spanners not fit the narrow grooves of HSA 835.
You can:
- Modify a common key (Most likely the cheaper and faster solution.)
- Order original tools (If possible via a local bike dealer.)
For original tools - Ming is using a special hook spanner for this purpose;
its unusual feature is a 1/2" square hole close to the key’s mouth.
You’re surely suspected already correct - yes, the hole was added for a torque key.
(Just don’t forget to calculate the new torque - force is out of centre 
)
According to my infos should Strida distributors be able to order tools;
if there is nobody (willing?) in your country please ask at the next one.
Recently I’ve ordered these; couldn’t find a combination of both.
They do not fit as they are, was too lazy to grind them by now 
url=http://www.werkzeug.edingershops.de/Schraub-Ringschluessel/Hakenschluessel/Gelenk-Hakenschluessel-60-90mm-mZapf-6mm-AMF::91178189.html Hook key 60-90mm[/url]
url=http://www.werkzeug.edingershops.de/Schraub-Ringschluessel/Hakenschluessel/Gelenk-Hakenschl1-2-Zoll60-90mm-m-Zapfen-AMF::91178193.html Hook key 1/2" 60-90mm[/url]
Edit:
Keys are not recommendable, there is a lot to grind!