Available in LEADTOOLS Medical Imaging toolkits.
DICOM Waveform Groups: Manipulating Channels
L_DicomWaveGrpAddChannel
L_DicomWaveGrpDeleteChannel
L_DicomWaveGrpGetChannel
L_DicomWaveGrpGetNumberOfChannels
L_DicomWaveGrpGetNumberOfSamplesPerChannel
L_DicomWaveGrpSetNumberOfSamplesPerChannel