It appears that the functionality to create a temporary file was omitted from Windows 8 / 10
If anyone knows this to not be the case then please add a comment to that effect.
Consequently, I decided to create a little helper method:
public static async Task<StorageFile> CreateTempFile(
StorageFolder folder, string extension)
{
string fileName = string.Empty;
while (true)
{
// Get a random filename
fileName = string.Format("{0}.{1}",
Guid.NewGuid().ToString(), extension);
// Check if it already exists
IReadOnlyList<StorageFile> fileList =
await folder.GetFilesAsync();
// If it does then loop until we have a unique one
if (!fileList.Any(f => f.DisplayName == fileName)) break;
}
var newFile = await folder.CreateFileAsync(fileName);
return newFile;
}