I'm interested in this as well because I run into the same issue. I have my container citrus on a drip system, especially in the summer, and I have to alternate hand watering to properly feed them. If your crops are short-term plantings you could mix in slow-release fertilizer when you make your potting mix, which would give you about 6 months of nutrients. But I don't think any fertilizer added as top-dressing would get adequately wet by the drip-emitters. I believe it's possible to add a liquid fertilizer reservoir to your actual drip system but that's a more costly and complicated setup.

A Fertilizer injector runs about $30 on amazon but liquid fertilizers need to be used. A brother uses one like I linked to and has no problems running liquid miracle grow through it and works well. They're not complicated in the least and there are many you tube videos showing how to use them. You can mix a water soluble dry fertilizer in water and dump in the injector if you like.

Or you can also use a Y screen filter Dump in your water soluble fertilizer at the water inlet or through the clean out plug at the bottom. The fertilizer will dissolve as the water runs through and out your emitters. (The fertilizer must be on the inlet side of the screen. )

I've found these for $6 in the irrigation section at home depot but all are a little small and larger ones can be found. Any Y screen strainer or T screen strainer can be used if it has a screen mesh inside.