I'm not sure it's possible to do exactly what you were thinking, but you can come real close (close enough to get the job done at least).
First, you probably have something like the following in your .zshrc:
bindkey '^r' history-incremental-search-backward
And a similar one for forward search. You need to change these accordingly:
bindkey '^R' history-incremental-pattern-search-backward
Now you can use patterns in your history searches. In this case, type control-r (for backwards search), then type something like the following (press control-r again once you're done to search for your pattern):
For "scp" OR "hello" anywhere in the string:
Starting with "scp" followed by "hello" anywhere in the string:
Not every pattern you can use for globbing works (for some reason it doesn't work if you try to do a strict "AND" search with two expressions where either may come first), but that should be close enough to do what you want.
Good question, by the way.