Yes it absolutely can be done and is preferred by many growers including myself. I don’t use spore syringes personally unless I purchase from a vendor and that’s all they have.
One can make LI or LC and it will work just fine and faster really because no germination needs to occur. Plus an added bonus is that you can strategically omit a bit of water from the cake material and add more LI/LC (what I prefer) for much faster colonization times without throwing off the moisture content of your substrate. Just make sure all is clean and free of contamination, and it will work like a charm.
I have done it that way for years when I make cake material. Case in point here is a PP5 container I did that very thing using LI (I like LI better personally, but just me).
I brought my material to just under full field capacity, i.e. you will hear a squishing sound and the substrate will hold its shape upon squeezing it, but NO water drips out and inoculated it with 20 ml of known, clean LI in 10 different inoculation points:
6 days later:
3 data later (9 full days since inoculation):
And finished result:
You must be very sure your LI/LC is clean before doing this and your sterile technique is sound, but once you do, the sky is the limit IMO. Also, as you can see, this was not a cube grow. This was a Pan isolate that I have worked on for a while. Do not expect those colonization times with cubes. Also, before adding that much LI/LC to the substrate, make sure you really understand field capacity and know what to look for. It’s ok if you mess up on the dry side. You can always add more water slowly and deliberately, but if you add to much water, then inoculate with that much, it could be disastrous.