Interesting method! lol Sounds like something I would do!!
If those objects needed to be used in a specific order, it is very easy. I would just create a new object when you use them together. For example, if "use light with pipe" is the first step in the process (and I'm assuming it is a tobacco pipe, not a plumbing pipe =) it gives the response "You have lit the pipe". Then move the pipe and the light source into an 'inventory room' and move an object called 'lit pipe' into the players inventory. If the player types "use light with lock", you simple add a response like "That makes no sense at this time." Then you can repeat the procedure with the next item. Use lit pipe on lock. Repeat with ice.
If the objects can be used on each other in any order, this becomes more difficult. I have lengthy thread where I had help solving this problem. I'll edit this post and reference that thread when I find it.
EDIT: Here is the thread I stumbled through with some excellent helpers solving the more difficult version of multiple item usage.
viewtopic.php?f=10&t=5411&p=37579#p37579Let me know if any of this is helpful. Thanks and good luck.
XanMag