Im afriad you will find it very very hard! I worked at a spread betting company and evey time you log into a live account they make sure its a non US Ip adress that you log in from. If its a US IP your account is automatically suspended. Also when you open a live account you need to verify the application by calling the company from a non US landline.
If its a US IP your account is automatically suspended
Like one of us, mentioned...that it is possible to get around this (in the context of advancement of internet, It became possible, ages ago.). If you do some searching on google you can actually do it free of cost.
Also when you open a live account you need to verify the application by calling the company from a non US landline.
Again there some IP/VOIP telecom service providers how can get you a uk landline number.
For ex: you give them your US landline number, they would give you a UK landline number. So on the application you can put the UK landline number. So when the company rings the uk landline number, its your phone in US which rings.
And there are companies which can show a particular number that You ask to be displayed on caller id of the called party.
So this takes care of the privacy issues (of sharing your personal details with others), the SB needs a uk landline number, you have a UK landline number to make and receive calls.
You may also want to consider opening a off-shore account (in USD or GBP) at a bank in the UK. ex: See
HSBC Offshore | Bank accounts, Savings, Investments, Premier Banking, Expat advice abroad
Basically, its almost impossible to spreadbet from the US.
For every "N" no. of rules, there are "N+1" ways to get around them. (Now don't bother to check how mathematically it is valid, as long as one can get the idea that every rule, potentially has a loophole)