1. There isn't a easy end-user way for this unless you have technical/IT knowledge.
2. If you do you nee to get the 2 networks onto the SAME network subnet because your printer is being assigned a IP address off the router with probably Cable/DSL/Fiber/Ethernet broadband versus the WWAN LTE connection.
3. In order to do this you need to replace that existing wired broadband router with one (or put it behind and possibly configure IP routing or double NATing) a new router than supports NOT the MiFi but a VZW WWAN card (The UML290 for example) + existing wired broadband and do seamless switchover.
4. You are better off disconnecting and reconnecting to print a document.
5. If you ARE AT HOME why not use the wired broadband connection which is UNLIMITED or very high (250GB+) and not worry about caps!?
I really appreciate the answer. I did find a Wireless Extender (NetGear Universal WiFi Range Extender WN2000RPT) at my local Best Buy and thought I would try it.
Just as you indicated in your reply, my existing router and the MiFi 4510L router are both configured to assign IP addresses, which results in conflicts. I know that it would be possible to configure both devices so that DHCP conflicts wouldn't occur, but it would take me a lot of time to learn how to do this.
Here is what I finally did:
1. Configure the WN2000RPT as a wireless bridge. The device has four ethernet ports, just like my current router.
2. Disconnect the wired devices from the router and connect them to the WN2000RPT.
3. Turn off the router.
4. When I initially installed the printer, I assigned it a static IP address that was beyond the range of the DHCP for the wireless router IP address assignments. I had to make sure that the static IP address was being referenced by the machines that were trying to print.
The MiFi 4510L supports 5 wireless connections. It also assigns 9 IP addresses. So, this means that it can support the four ethernet connections on the WN2000RPT, in addition to the 5 wireless connections it already supports. One wireless connection (and IP address) will be used by the WN2000RPT. However, the WN2000RPT also sends out a WiFi broadcast, so the wireless devices can connect to it, also. This means that the MiFi 4510L - WN2000RPT combination will support 8 devices on my home internet, without configuring subnets.
BTW, I intend to replace my current wireless broadband service with the Verizon 4G service using the MiFi 4510L. The limits, speed, and price for my current wireless broadband service are nearly identical to those for the Verizon 4G service. This means that I can have essentially the same home Internet service with the addition of being able to take the MiFi 4510L on the road. I am not depending upon the home internet service for business usage, so it's ok if there a few glitches while Verizon is rolling the 4G out.