How to force Adobe Media Encoder to use 100% CPU and memory?
There might not be a way.  Based on your description of the problem, it sounds like the processing is the slow part.  While the video encoder itself is able to do multi-threaded processing, the image processing you are doing may not be able to.  By default, Premiere has always done as much parallel processing as possible for me and I frequently see it hit 99% CPU usage on my hyper-threaded quad core desktop.

The problem is most likely that some of your effects require the result of the previous frame to begin processing on the next frame.  If this is the case, there isn't an easy way to break it down across multiple threads and that would make it impossible to hit 100% CPU usage on a multi-core computer.

Similarly, RAM wouldn't be expected to cap on encoding as it is a stream operation.  There are some things that may need to be tracked over time, but for the most part, it is a stream operation with data going out as fast as it comes in, so there isn't much accumulation of data.

There are two main things that can improve the performance.  The first is GPU processing.  General purpose CPUs aren't really ideal for many audio/video processing tasks.  They are designed for doing a wide variety of general purpose operations, but aren't super efficient at basic operations.  GPUs, on the other hand, are designed for doing simple operations very quickly.  They can often reduce video processing tasks quite a bit.

A further improvement can be found in purpose built hardware.  There are professional cards designed specifically for processing video and provide real time processing and encoding of video.  These are often included in high end professional video editing workstations, but the price can be quite high.  It isn't unheard of for a professional video editing workstation to be able to get up in the $15,000 to $20,000 range or even higher, just for hardware.  They can go for a lot less if you don't mind waiting for renders (I work on a $2,350 system for my video work) but they can also get very high.