Do you have a 545 holder? If you do, you just need something to support it under the enlarger with anything that's handy, like a box or a book.
Alternately, you could illuminate the slide, say on a light box or even your enlarging head and photograph it on Type 55 with the holder in your 4x5" camera. The best way to do this with the enlarger might be to put the MF slide in the neg carrier, leave the enlarging lens in place but remove the camera lensboard, turn the enlarging head horizontal if your enlarger can do that, set the camera up on a tripod so that the slide is projected on the groundglass and make sure everything is aligned properly, focus using the enlarger bellows, and shoot. You'll need to make some tests to determine the best exposure.