Crystal malt has no diastatic power - it has no enzymes to break down the starch to shorter chain sugars for fermentation. If you want to get some sugar from the crystal, you need to do a mini-mash with some base grain like 2 row. All a steep is going to do is add colour - which could be a lot if you add 2lb.
So, to answer your question - no it is not a satisfactory solution to prevent drying out the beer.
If you can get hold of 2 row as well as crystal, just do a partial mash and forget the dextrose. Partial mashing is exactly the same as steeping - just hold the grain in 150F-ish water for 30-60 minutes.
Note that the potential of grain is going to be modified by your extraction efficiency, while the potential of DME or dextrose is not.
So you need to get 88 points to make up for the 2 lbs of DME you are short, right? [Take the last two digits from the potential, x 2 for 2 lb.]
Assuming an efficiency of 60% for a partial mash, and a total potential of 35 per pound of grain
0.6 * 35 = 21 points per pound of grain actually available.
88/21 ~ 4 lb of grain total.
So do a mash with a total of about 4 lb of grain. You want mainly 2 or 6 row, with just enough crystal to give the color you desire. Plus - you need at least 1 lb of base grain per lb of crystal to get conversion.