Never faced this challange but I'll toss out some ideas.

Funnel fill a wine bottle and dispense with your thumb regulating the flow.

Grab a handful and dribble it out with a release of your grip.

Line up the pots and run over them with a drop spreader once or twice. Use stacked 2X6's under the wheels for clearance. Sweep up the waste and refill the spreader.

Hand toss at the pots, sweep up the waste and toss some more.

Switch to liquid fertilizer and hose end sprayer.

I'm ouy of ideas, sorry.

Sherwood,
Have you seen this backpack granular dispenser? Seems to accomodate your program requirements. The units are patented and distributed in the US (see Fertil Dispenser link below) but are available in Canada as well from this link:

http://www.rittenhouse.ca/asp/Product.asp?PG=2018

Looks like you'll pay a premium for it up there though.

Here is a link that might be useful: Fertil Dispenser