I've decided to use my 18-ounce aluminum fuel bottle as an oil dispenser.
It fits perfectly in my bottle cage, so no need to carry it in my backpack or leave it at home. Since my four-liter fuel tank holds enough gas for 8-9 days, the fuel container doesn't get used at all. I measure & add 1.875" ounces and just leave it there, until fillup time. This is for 3 quarts @ 50:1 f/o ratio. Adding four quarts is ALWAYS a freaking mess. I MIGHT mix oil/gas, then pour it into the tank while filling up. That'll do for now.
Later, I'll drill a hole into the fuel bottle's cap and screw in a threaded petcock. I'll prolly need a vent hole too. Then I'll weld a bung onto the fuel tank, or bolt one on.
THAT should do the trick, and for cheap! I just need to buy a petcock and the bungs.