You can setup the PSTN Caller Default DP (Dial Plan) to automatically dial the voip leg of the call when the SPA3102 answers the incoming PSTN Line call. For example a dial plan of (S0<:19251234567) will automatically send the stated number to your configured proxy server.
If your question is, however, can you automatically dial dtmf digits after the voip leg of the call connects I do not know of any way to do that.