My previous method stopped working with Windows 10, fortunately I found another workaround on the Microsoft Forums as follows:
It looks like the OneDrive client in the RTM version of Windows 10 does not allow syncing OneDrive to an SD card via the empty NTFS folder method if there isn’t enough free space on the C: drive for the data to be synced. There is a simple workaround from GiovanniSantoroJunior:
From the Disk Management console, follow these steps:
1. Right-click Disk Management and then click Create VHD. Follow the prompts that appear.
2. Right-click the new disk and then click Initialize Disk. Click OK.
3. Right-click the new disk and then click New Simple Volume (or select a different volume type, if available). Follow the prompts that appear.
Follow these instructions to set your new VHD to automount when Windows boots.