T-SQL (SS2K8) :: Skipping Group With FOR XML Path

I have a table with a text field and a grouping number.

1, A
1, B
1, C
1, D
1, E

2, A
2, C
2, D
2, E

3, A
3, B
3, C
3, F

4, A
4, B
4, D
4, F
4, G

I assemble the text fields into strings by group, using the FOR XML PATH('') function, so that I end up with

1, A-B-C-D-E
2, A-C-D-E
3, A-B-C-F
4, A-B-D-F-G

This all works fine. I now have a requirement to leave out some groups, based on whether the GROUP does or does not contain a certain text. For instance, if I want only GROUPS with 'E', my result set should be

1, A-B-C-D-E
2, A-C-D-E

If I want only those GROUPS that DO NOT have 'E', my result set should be

3, A-B-C-F
4, A-B-D-F-G

I can (and have) put a condition on the assembled string, but it seems to me that it should be possible to make the cut earlier. That is, rather than assembling the string, scanning it with a Like '%E%' condition and discarding what doesn't meet my needs, I would like to stop scanning the incoming GROUP as soon as a mismatch is detected.

If I want all groups that will not contain an 'A', for instance, it is pointless for the query engine to read in 'A', 'B', 'C', 'D', 'E', put them all together into a string, compare it with a wildcard and throw it away. As soon as it sees the 'A', it has enough information to completely skip over the rest of that group. The abbreviated examples here are trivial, but the real code is not.

All I've been able to dream up so far results in skipping the RECORD that contains the 'A', but not the entire group.