Creating orchestral accompaniments for solo piano performances of concertos is challenging, especially when aiming for a system that adapts to the pianist's tempo and dynamics. In this work, we present a semi-automatic offline approach using source separation, alignment, and time-scale modification techniques to generate orchestral accompaniments from public-domain recordings. Our approach separates the orchestral part, aligns it with a new solo-piano performance played by the user, and adjusts the tempo and dynamics to match the user's interpretation. While some processes are automated, significant manual adjustments are needed for temporal alignment and sound production. Our results demonstrate the feasibility of this method while highlighting the need for further automation. We have made the multi-track recordings of the created mixes publicly available for research purposes at https://www.audiolabs-erlangen.de/resources/MIR/PCD_AudioLabs.