Low flow bathroom appliance doesn't activate tankless heater
Thanks to MonkeyZeus suggestion. Here's the answer I'm trying. If you look around you can find a 12VDC Circulation pumps that do 2 GPM for under $50.
Simply install an outlet in a location safe from water near the appliance or fixture that has some means to control it whether a switch or motion sensor.
Install the pump between hot and cold lines. Plug the Pump's AC adaptor into the outlet mention above. And life is good. A bonus is no water is wasted getting the water heater up to temperature.
Edit: I'll mark this as correct once I have mine installed and made sure it's working good.
Update: installed and working good!
I used these parts:
1/2&quot; Back-Flow Preventer: https://www.amazon.com/gp/product/B000EDUTN6
Hot Water Heater Circulation Pump with DC Power Supply Adapter 2.1GPM: https://www.amazon.com/gp/product/B01G305PK0
The incoming hot water line is 1/2&quot; pex, going to the bidet, and the out going cold line is 3/4&quot; pex, because the shower line was easier to connect to for that. Per the comments, I added a backflow preventing valve. The pump didn't come with one.
You can hear the pump running, and once it kicks on there's hot water in the line in less than 20 seconds. Works so good I'm going to install one on the kitchen faucet.
The pump it's self is submersable, 12VDC, and low amperage. Parts including the pex connectors, crimps, and such was less than $50 and took less than an hour to do. Most of it was figuring out the in and out on the pump.
The install is less than 10 feet from the water heater, so this may not work for longer runs, or narrower pipes, or some other variables. I mention this because the pump isn't rated for longer runs. It works good for my loo, that's all I know.
Haven't yet put the motion sensor switch and outlet in yet, but I'm confident about those.