Hi Nicolas,
REST implementation (at least in 9.8 version) is more based on convention than on enforced rules.
This is not a bad thing because as a style REST is more “loose” than others.
Anyway, it might be as simple as defining a new input for the IS service that you expose.
I find this blog post very good and always reference it when dealing with REST cases: How to create a REST service in webMethods Integration Server - SOA rocks!
Go ahead an check it.
Let us know if it worked.
#Integration-Server-and-ESB#webMethods