What you are trying to do here is a little more advanced then most novices with DSLRs do. This is not to discourage but to encourage as by stretching we learn. You are learning more about metering and you have to know about the exposure triangle of shutter speed, ISO and aperture to trade each off against the other to get what you want.
aleonx3's suggestion of using multiple exposure (2-4 exposures should do it) has more then a little merit. It is a tool the K-5 ( it can do up to 9 in camera) gives you for things like this. I often use it myself but as aleonx3 pointed out you will need a tripod. From my experience even with a good tripod you will need to use some kind of shutter release as without it you will end up moving the camera. It could be an IR remote but you will have to set up the camera for IR use before you do the multiple exposure setup. You don't have to get an IR you can use a cable release and later this will come in handy if you decide to start using bulb mode. Here is an inexpensive one from B&H
Dot Line Remote Release DL-1490 B&H Photo Video. There are all kinds of these you can use but I have played with this one and for the price it is OK. If you get into this later you can get a really fancy one with timers and things like that but this is a good one to start with. A tripod and remote release will come in handy not only for this or if you decide to use a ND filter but for other things later.
One thing about using multiple exposure is you can get ghosts. This can be a good thing if you want them but if you don't you will have to be on the look out for them.
DAZ