If you use webMAN MOD, press SELECT+O to unmount the game currently mounted.
That action also remaps /app_home to /dev_hdd0/packages, so you can use the option Install All Packages that is available when you press TRIANGLE on Standard menu of Package Manager > Install Package Files
Another option is to use the web command: /install_ps3<path>
Where <path> is the full path of any directory in the internal HDD or any USB directory in FAT32
To install multiple packages in NTFS/exFAT it is required to create an ISO with all the packages in the root of the disc image.
Another option is to mount /net0/PKG using ps3netsrv and use Install All Packages