Last time I got asked this query was a while ago and at that time I couldn't find any online trading account that could be set up in the name of a corporate entity such as a pension trust. They all only facilitated personal account-holders.
Standard Life's Self-Directed offering allows trades to be made over the phone which can then be viewed online, but I know that's not the same as what you're asking.
If there is an online stockbroking account that can be opened up by a pension trust, I'd be interested to hear about it myself.