If you are using manual bookkeeping system then you can have a separate collumn for privately paid expenditure.....so you have 3 ......Cash .....Bank ....and Privately paid.
If you are using Simplex D Cashbook there may not be space to do that. However you could write them in in a different colour and do two subtotals at the bottom of the page....using say the cash collumn.
Or like dee says you could draw the money out as a cheque or cash and analyse the expenditre to what it was paid for.
You could even do a "ghost entry" as follows:-
Post in cashbook as cash expenditure analysing between what you spent it on......then post an amount as sundry cash receipt as capital introdroduced from you to cover the amount of the expenditure. As if you actually put the cash in to the business to pay the expendite. The transaction will balance out.