the Mnk
I'm not really making examples as of late, but two ways come to mind:
1.
you could make a second paster and set that to the size you want, then position that over the part of the tilemap you want, paste the tilemap, then paste that paster to the other one.
2.
another idea is to utilize the draw quad actions. You define the four corners, and the uv's of them of the texture of some object. More math to figure out beforehand is needed for this, and it would only work if you can grab the tilemap's texture, I don't think you can though.
Hopefully that can give some idea's. I haven't verified any of it so I may be off here and there.