Yeah the link Coro put up has an example of net_package_install in post #3. That thread was slightly different as I was trying to run it from USB but the principle is the same and this could be added to any category xml so only 1 modded file on OFW flash was required.
Important bits in bold:
EDIT: Some limitations of the net_package_install method:
- Retail packages only (unless other patches are applied of course)
- The LONG Content ID in the XMBML (content_id string) must match the package.
- The title on the XMB will just say "Install", or you can use any other system text from inside the main explore rco, "msg_install" was the most suitable one I could see there as there is nothing similar to "download". As a workaround I normally put the "install" item inside a sub folder that has the name of the package on it. Just adds 1 extra press of X to the install process.
- The prod_pict_path is for the icon and it will ONLY work with local paths, So we can not use icons from inside rcos, or URLS to hosted icons like in other places. To avoid having no icon here the easiest thing is to pick one from dev_flash\vsh\resource\explore\icon\ like fah-xmb.png
- XMB must be reloaded after adding this entry to an XML.
My guess is that the XMBML class
type:x-xmb/xmlpackagefolder is blocked on OFW as its not required for anything and was a security risk. However the XMBML class
type:x-xmb/xmlnpsignup still allows packages to install as its needed in a few places on the XMB like the Photo Gallery add on, and historically PS Home/FAH.
Side Note: If installing from webserver suits you, There are 2 other ways that will still allow packages to install without any sprx patches, and that is via the xil xmls (eg spotify) and the nsx xmls (eg Whats New). In the past these required a PSN account, but something changed around 4.83 IIRC and now if you have no PSN account when you try access Whats New, it gives you the option to enable those features by putting in your region and age. These methods have lots of disadvantages, but also some small advantages vs net_package_install such as icons and titles working properly.
I guess Sony did that because they finally realized they were missing out on pushing adverts to the millions of consoles that have no PSN account.