From HolisticFerret. Copied for ease of viewing.

"If you suspect your ferret has eaten something they shouldn't, do not "wait and see". Immediately start this process to push through whatever the problem may be. Pumpkin and vaseline are only to be used in emergencies, and vaseline can and does affect nutrient absorption. However, better a few days of possible upset tummy than the alternative. The blockage protocol is:

• 1 tbsp 100% pure canned pumpkin

...followed one hour later by...

• 1 tsp vaseline or ferret lax

Alternate these both hourly until the ferret has a nice big gloopy orange poop (should take 2-3 hours).

This should only take about 4 hours total. If at any point during this protocol the ferret begins vomiting, or crashes, stop immediately and call the vet while you are on your way there. It has now become a total blockage and the ONLY thing that might help it pass is a barium xray. If the barium doesn't push the obstruction through then immediate surgery is essential or the ferret WILL die.

If the ferret does pass the object, follow up by 1 tsp of pumpkin for 3-4 days to be certain everything has gone through."

Info found here curtsey of Holistic Ferret.

From the link:

Homemade FerretLax (ditch the sugary crap!)

1.) Get a small container of Plain Vaseline (100% pure petroleum jelly) and some Salmon Oil.

2.) Scoop out about 1/4-1/3 of the Vaseline to make room in the tub (if not, be prepared to spill!)

3.) Pour in salmon oil a little at a time and mix into Vaseline until you reach a creamy, but still paste-like consistency

I used roughly 1/8-1/4 Salmon Oil:Vaseline (I didn't measure though, just added and mixed until I reached a consistency I liked). The mixture should smell slightly of salmon oil.

Voila! Homemade, healthy, effective ferret laxative!