You should be able to do this by adding a setting to your <worklet> settings in config.xml. Add the following setting:
<num-transaction-threads>1</num-transaction-threads>
The JVM will still have multiple threads (for garbage collection, JIT, etc.), but Chauffeur will only run transactions in a single thread in each Client JVM.
In many cases you'll also want to set:
<max-per-client-users>1</max-per-client-users>
This will limit the number of Users (which are often used to hold per-user session data). Chauffeur will ensure that any user will only have one active transaction at any given time, so either one of these settings will generally work. I almost always set them to the same value.