How can i Decode a part of a turbocode using viterbi decoder

hello,

i'm writing a programme to simulate the behaviour of Turbo Code in cooperative communication, for that i need to isolate the systematic bits and the first parity bits (wich i did) and then transmit them to the partner. when the partner receive those bit it should decode them but, the turbo Decoder can not be used here because the partner has only the systematic and the first parity bits. so my question is : can I use the viterbi Decode or the APPDecoder to decode the received bit ? if yes how can i do it ? if no what can i do? i'm using the Communications System toolbox in matlab R2014a.