Hi,
Unfortunately it is not possible to make the modification for the accelerated display mode.
This leave two options:
1. Use an ArcGISLocalTiledLayer (as suggested previously - but I cannot recall why this is not a viable option in your solution). They can take some time to generate and do take up more space on disk but the performance benefits typically far outweigh these downsides.
2. Try the new .NET SDK beta which should handle these frequent pan requests more gracefully (but still will not generate a larger dynamic layer image extent than the extent of the map). Again in this case we advise using an ArcGISLocalTiledLayer for a seamless panning experience.
We are aware of the drawbacks of Tile Packages and on the longer term roadmap for the new .NET SDK we are looking at introducing vector basemaps which will combine seamless panning and richer dynamic rendering with a smaller disk footprint and reduced generation time.
Cheers
Mike