freeradius-proxy with Rlm_cache

Hi, We would like to configure a freeradius proxy-server v. 2.2.0 under RHEL6 with users caching. The scenario we would like to achieve is the following: 1. client sends username/OTP to freeradius-proxy that relays to central radius server. Central radius server accepts and replies to freeradius-proxy that relays to client. 2. client sends same username/OTP within TTL to freeradius-proxy that accepts and replies to client. This should be possible using Rlm_cache module but we did not find a proper how-to for configuring this. Any help much appreciated. Dominique