A comment to another question of mine asked me "Do you know any separable loan word?".
I can't think of any, off-hand. Are there any? One would be enough to answer the question.
As you can infer from the other answer and comments below, we would have to narrow down the definition of a loan verb.
If it were sufficient enough that the root of the verb is not of Germanic roots, then there are certainly verbs.
All these seperable verbs, however, have a Germanic prefix. These are not pure non-Germanic verbs and to my mind we should rather take a look at verbs that have foreign prefixes. Pure non-Germanic words.
Having taken a look at the list of foreign prefixes on canoonet, I can't think of any verb with those prefixes that is separable. I dare say there is no such a verb.
Not everywhere accepted and even the non-separable version might be more common, but it seems that
updaten (z.B. Sie hat ein paar Anwendungen upgedated)
is a good candidate (whether it's good German, that's another story).
Not from English, but from Latin:
"Mauer" is a loan word, coming from Latin "murus". If you want a more recent borrowing, take
"Downloaden" and "uploaden" are mentioned by Wikipedia as separable verbs sometimes.
Something of interest is that there are plenty of verbs that have been borrowed from English that, whilst don't have a separable prefix, have an inseparable one whose stress doesn't lie on the first syllable and thus does not take "ge-" in the past participle.
Examples off the top of my head include: