Greetings Simon,
You could turn on an EndNote output style setting called “Grouped References” - this would output a bibliography in which multiple references can appear on the same line. However, you wouldn’t be able to sequentially number the references, as shown within your example. Instead, all references would have the same bibliography number. Aside from all references showing the same bibliography number, there is another numbering option called “Composite Citations” , in which each reference would be assigned a unique letter. For example, with these two style settings enabled, your reference list would be numbered 1a, 1b, 1c, 1d, 1e, etc. Let me know if you’d like to explore this solution further and I’d be glad to provide the associated instructions for editing an EndNote output style in this manner.
However, if the numbering format described above would not be suitable, the only other way to achieve the desired format would be to perform a Find/Replace in Word after the final formatting of your document. Before performing any global edit, I would suggest saving a backup of your Word document. Afterward, you can highlight your formatted bibliography and access Word’s Find/Replace command. You’d instruct Word to search for paragraph marks and then perhaps replace that with a single space.
Please let me know if this works for you.