You may not have room for a dedicated sharpening station, but that doesn't mean that you should rule out sharpening.
If you are concerned about the finished surface on pens, the best tool for the job is a skew. And you don't need a grinder to sharpen a skew. In fact, a grinder may be exactly the wrong way to sharpen a skew.
One option is the possibility of using your lathe to sharpen tools. You can pick up a 5" sanding mandrel at Harbor Freight, Home Depot or Lowes. The challenge is to figure out how to mount it on your lathe. If it comes with a shaft, you can use a chuck. Another option, however, is thread a block of wood to screw onto your lathe spindle (if you don't already have a spindle tap, you can get one at Ace Hardware for about $20). Then, attach the sanding mandrel to the block of wood so that you can then use ordinary sandpaper to sharpen your skew. Actually, you can sharpen any turning tool other than scrapers with that sanding mandrel.
And if you want to get fancy, you can make a sanding mandrel from a scrap of MDF that you mount on the handwheel on your headstock - that way, the mandrel is always in place so you never have to dismount the workpiece to tune up your edges.
The other option for skews is that once you have used sandpaper to get the shape you want, you can sharpen the edge using a diamond hone. Diamond hones come in various sizes - small paddles, the credit-card size that is fairly popular with some turners, and Harbor Freight even has larger hones that are fairly inexpensive. If you use a diamond hone to sharpen your skew, its advisable to use some kind of lubricant - tap water with a couple of drops of dishwashing detergent works just fine. I use a credit-card sized hone exclusively to sharpen my skews - it takes no space at all because it lives in the pocket of my turning jacket.
