I figured out that one possible way to achieve this would be to make all accounting data publicly available on the internet - this would open the door for peer review. There is always a problem of incompatible data formats, but this could be overcome by defining some simple, possibly XML-based, data format. The progress in defining an XML-based EDI format could possibly contribute here.
The next question would most probably be: who would be motivated to do this peer-review? I can imagine several possible parties:
- concerned citizens, in the case of governmental organizations
- students, in all possible cases - the universities/colleges very often give assignments in the form of "case studies", this could be turned into "go and find some fraud" assignments
- audit companies that are paid to do the audit - the audit results should also be published online so everyone can see for themselves that the audit was thorough
But how should we kickstart this process? I bet no corrupt politican wants to have this kind of peer-review. That will be up to the non-corrupt officials to decide.
UPDATE: 7 years later (2012) and we have some progress on making this idea a reality (as part of OpenData movement, see also opendata.ee). Riigipilv.ee publishes all accounting data of Estonian municipal governments.