Use Fortigate as switch vs Cisco 2911

So here's the context:

At remote office with 5 people, I have a Fortigate 80e with 14 open ports as the main router/firewall. Below that, I have a cisco 2911 with a switching module with 15 ports being used (this router used to be used for PRI phone connections). The problem is that the switching module is only 10/100. This 2911 is also the DHCP Server for voice and data subnets. This office decided to purchase 300/30 Mbps internet without consulting us but doesn't want to purchase a gigabit switch to make their lives easier. So I'm stuck with what I have. Here's a quick Visio diagram of the setup:https://i.imgur.com/1NsL5Jh.png

So here's what I'm thinking. Since the Fortigate doesn't have enough ports, I can use the 2911 switching module for the printers and move everything thing else to the Fortigate. My question is, how can I use the Fortigate ports as a "switch" when the DHCP server is on the 2911? Should just make the Fortigate the DHCP server, and the 2911 a "dumb" switch?

Or should we just push them to buy a gigabit switch?