Concatenate two S1 TOPS SLC products

Is there a tool to merge two S1 IW products along a track before processing? Basically we need to merge the geotiff files and the XML files to make a new product. WE don’t actually use SNAP for InSAR processing so am looking for a tool that provides the original format on output.

We don’t have anything that will write to the Sentinel-1 SAFE format.
You can use the S-1 Slice Assembly tool to concatenate products together but you will need to save as DIMAP or BigTiff.

There is a command called

gpt SliceAssembly

that looks promising. I tried to run it from the SNAP GIU and there was a Geotiff-XML output option but the job failed at the 4 Gbyte limit. What we really need is a way to do this on a pair of along-track XML and geotiff files. The most difficult part is to merge the two XML files. We don’t need to rebuild all the directory structure of the SAFE product.