Is it practical to use a stream cipher in a block cipher mode? My idea is to use a stream cipher encrypting 16 bytes at a time as a primative block cipher in a mode of operation such as CBC mode.  Is this practical or useful in any way?
The way you propose to use a stream cipher as a drop in replacement for a block cipher is flawed, as the other answer explains nicely.

There is a simple way to convert a stream cipher into a block cipher. In pact, it works for any PRF, regardless of if it is reversible or not.

This presentation perfectly covers how to use a PRG such as a stream cipher to construct a block cipher.

Basically, you use the stream cipher in the following manner:

Take your message m and break it down into an n-bit binary string.

Take your stream cipher $G(k)$ and use it to generate a a stream of length $2 · |k|$. So $G(K) \to K^2$ (output space = double that of keyspace).

Do $k \to G(k)[0]$ and $G(k)[1]$, pick $G(k)[x]$ depending on what the first bit of m is.

Then, compute $G( G(k)[x] )$. You have a message of length two blocks, pick the block corresponding to the second bit of m. Repeat n times.

This can be reversed (decrypted) in the same way Feistel networks are, via the Luby-Rackoff theorem.