Do no train companies offer corporate accounts?
I remember reading on the East Coast website in January 2015 (VTEC took over in March that year) that they had a business travel portal that was going to be launched soon. That message soon disappeared off the website and it looks, for whatever reason, VTEC canned the project (perhaps they had other plans or the portal was just rubbish). The ticket wallet app released by VTEC was also started by East Coast but wasn't ready in time. I hope VTEC are planning on a new app as Ticket Wallet is dreadful.
One small company I worked for used to book tickets through a single EC account (to get rewards) the management had their company cards linked to the account so the appropriate one was selected and if less frequent travellers were set up to use self print tickets (if available) or post if not. The £1 postage fee and the value of rewards meant it was a lot more cost effective than using a TMC but can only scale to relatively small companies. I wonder if they're still using the same method now, less reason to but they're used to it and it saved on fees.
Back in the East Coast days you could earn EC Rewards booking through the trainline business site (at a reduced rate than booking direct). The instructions were to add your email address to the loyalty field of the booking page. Does anyone else offer rewards to business travellers or was this field solely to support EC?
If you need any card collection through the VTEC website a workaround is to buy a gift eVoucher for the amount of the journey (I think a partial amount also works but not 100% sure) - if you select 'other' amount you can buy a voucher for the exact price. Anything paid with a voucher is any ticket collectible. Also adding free tickets to the booking, if they're giving out any free surprises anymore, also triggers any ticket collection.
On the trainline app using Apple Pay will trigger any card collection as well as PayPal mentioned above.