The trick is in drawing a natural-sounding glissando, and that takes practice.
My method:
Choose start and end points by determining the interval of the slide, which is often a quarter or half note in duration. Insert three points - at the start, middle and end - and listen to the result. Of course, it will sound choppy at this point, but the idea is to verify that the slide begins and ends at the most natural-sounding times. Then fill in the gaps between those three points. It won't ever be a straight line you want. Most of the time it will either be a single logarithmic curve (like the "slow" curve in SONAR's automation or slip-edit options) or a dual-log "S" curve (like a combination of the slow automation curve followed by a "fast" curve).
How many points you need to draw in will depend on the instrument. Some instruments smooth the points out on their own and might only need a few values, while others require denser grouping to avoid a zipper effect. But you will never need to draw as many points as a recorded wheel sequence would have generated.
So yeh, it's do-able. Even though it's more work, you can actually get better results this way than recording the wheel because it will be musically more precise.
Oh, another tip: it can be tricky translating a wheel value to a note interval. There are 8,192 possible values in each direction. Your instrument definition will determine what pitch interval that represents, so it's best to tell the instrument that the pitch range is the largest range you'll be using in the song. So if your slide is, say, 4 semitones, adjust the instrument's pitch range to 4. Then, a value of -8192 will be your starting pitch and each semitone will be at intervals of 2048.
Example: the slide goes from C to E. If the MIDI note played is E (the ending note), the first pitch wheel event would have a value of -8192, the last a value of zero. In between, -6144 will be C#, -4096 will be D, -2048 will be D#.