Reducing Filter Flow

Two of the tanks that I bought used came with oversized internal filters. The tanks are each about 110 litres, the filters are Fluval 4 Supers (NOT U4) which I understand have a flow rate of about 1,000 l/hr. Even though it is possible to reduce this rate with a control lever, the slowest rate still seems to me far too fast for the fish I intend to put in the tanks. In addition, the usual floating plants I like to have in every tank just fall to pieces. It takes less than two seconds for water from the filter outlet to reach the other end of the tank, about 75 cms away.

They are good filters and I'd like to use them, but I was wondering if I can reduce the flow rate. Internally, the media holder divides into two vertically, and each side has a piece of sponge, i.e. there is a left and right sponge, not top and bottom. I was thinking about cutting a few centimetres off each sponge and filling the space with tightly packed filter floss. Water flow through this should be slowed down, I would hope.

Anybody else have any ideas? Of course, it may just slow down as the sponges clog up, and if I'm not too meticulous about cleaning them.

I use the sponge or filter wool over the outlet method if I need to reduce the flow (if I use the aquaball filter in the quarantine tank for instance). Make sure it is attached very securely as the water flow can dislodge it if not done properly.

Thanks for all the ideas. For the present, I've just attached a piece of filter wool over the outlet and that has dispersed the outlet flow considerably, which is basically what I wanted. The only problem is that both impellers are now making considerably more noise. This is not a problem to me as these tanks are not in rooms where I spend much time. However, I was wondering if the effort of trying to push the water through a restricted outflow might be putting more stress on the motor?
Unfortunately, these filters do not have spray bars. On others, I have used the spray bar upside down from normal. The spray bar is below water level and the holes are directed halfway between up and forward. This produces a more gentle flow, as it is coming through a number of exit holes, but being also directed partly upwards, there is a nice level of surface disturbance which must be good for gas exchange. It's also virtually silent, important with five tanks in the living room!
With all the different filters I have, I do wonder how important the flow rate really is. These two have much bigger sponges than some others I have and the media volume must surely be at least as important?