"Download Accelerator Plus" supports resuming downloads for servers that do not allow a download to be resumed. I am not sure how this works. I assume the file is downloaded to Speedbit's servers and then "Download Accelerator Plus" download the file to the users hard drive. Free Download manager could download the file to Dropbox, Google Drive or some other online storage website and then download the file from the cloud to the users hard drive.
www.speedbit.com/dap-help/download-accelerator-always-resume/